diff mbox series

[v6,1/5] dt-bindings: PCI: brcmstb: Add brcm,enable-l1ss property

Message ID 20230623144100.34196-2-james.quinlan@broadcom.com
State New
Headers show
Series PCI: brcmstb: Configure appropriate HW CLKREQ# mode | expand

Commit Message

Jim Quinlan June 23, 2023, 2:40 p.m. UTC 
This commit adds the boolean "brcm,enable-l1ss" property:

  The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs --
  requires the driver probe() to deliberately place the HW one of three
  CLKREQ# modes:

  (a) CLKREQ# driven by the RC unconditionally
  (b) CLKREQ# driven by the EP for ASPM L0s, L1
  (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS).

  The HW+driver can tell the difference between downstream devices that
  need (a) and (b), but does not know when to configure (c).  All devices
  should work fine when the driver chooses (a) or (b), but (c) may be
  desired to realize the extra power savings that L1SS offers.  So we
  introduce the boolean "brcm,enable-l1ss" property to inform the driver
  that (c) is desired.  Setting this property only makes sense when the
  downstream device is L1SS-capable and the OS is configured to activate
  this mode (e.g. policy==powersupersave).

  This property is already present in the Raspian version of Linux, but the
  upstream driver implementation that follows adds more details and
  discerns between (a) and (b).

Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
Reviewed-by: Rob Herring <robh@kernel.org>
---
 Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Lorenzo Pieralisi Aug. 21, 2023, 2:46 p.m. UTC | #1 
On Fri, Jun 23, 2023 at 10:40:54AM -0400, Jim Quinlan wrote:
> This commit adds the boolean "brcm,enable-l1ss" property:
> 
>   The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs --
>   requires the driver probe() to deliberately place the HW one of three
>   CLKREQ# modes:
> 
>   (a) CLKREQ# driven by the RC unconditionally
>   (b) CLKREQ# driven by the EP for ASPM L0s, L1
>   (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS).
> 
>   The HW+driver can tell the difference between downstream devices that
>   need (a) and (b), but does not know when to configure (c).  All devices
>   should work fine when the driver chooses (a) or (b), but (c) may be
>   desired to realize the extra power savings that L1SS offers.  So we
>   introduce the boolean "brcm,enable-l1ss" property to inform the driver
>   that (c) is desired.  Setting this property only makes sense when the
>   downstream device is L1SS-capable and the OS is configured to activate
>   this mode (e.g. policy==powersupersave).
> 
>   This property is already present in the Raspian version of Linux, but the
>   upstream driver implementation that follows adds more details and
>   discerns between (a) and (b).
> 
> Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
> Reviewed-by: Rob Herring <robh@kernel.org>
> ---
>  Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> index 7e15aae7d69e..8b61c2179608 100644
> --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> @@ -64,6 +64,15 @@ properties:
>  
>    aspm-no-l0s: true
>  
> +  brcm,enable-l1ss:
> +    description: Indicates that PCIe L1SS power savings
> +      are desired, the downstream device is L1SS-capable, and the
> +      OS has been configured to enable this mode.  For boards

What does this mean ? I don't think DT properties are supposed
to carry information related to how the OS is configured.

Again - it depends on what DT should be used for, I am not claiming to
have any authority on that, just asking.

Thanks,
Lorenzo

> +      using a mini-card connector, this mode may not meet the
> +      TCRLon maximum time of 400ns, as specified in 3.2.5.2.2
> +      of the PCI Express Mini CEM 2.0 specification.
> +    type: boolean
> +
>    brcm,scb-sizes:
>      description: u64 giving the 64bit PCIe memory
>        viewport size of a memory controller.  There may be up to
> -- 
> 2.17.1
>
Lorenzo Pieralisi Aug. 21, 2023, 3:41 p.m. UTC | #2 
On Mon, Aug 21, 2023 at 11:25:11AM -0400, Jim Quinlan wrote:
> On Mon, Aug 21, 2023 at 10:47 AM Lorenzo Pieralisi
> <lpieralisi@kernel.org> wrote:
> >
> > On Fri, Jun 23, 2023 at 10:40:54AM -0400, Jim Quinlan wrote:
> > > This commit adds the boolean "brcm,enable-l1ss" property:
> > >
> > >   The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs --
> > >   requires the driver probe() to deliberately place the HW one of three
> > >   CLKREQ# modes:
> > >
> > >   (a) CLKREQ# driven by the RC unconditionally
> > >   (b) CLKREQ# driven by the EP for ASPM L0s, L1
> > >   (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS).
> > >
> > >   The HW+driver can tell the difference between downstream devices that
> > >   need (a) and (b), but does not know when to configure (c).  All devices
> > >   should work fine when the driver chooses (a) or (b), but (c) may be
> > >   desired to realize the extra power savings that L1SS offers.  So we
> > >   introduce the boolean "brcm,enable-l1ss" property to inform the driver
> > >   that (c) is desired.  Setting this property only makes sense when the
> > >   downstream device is L1SS-capable and the OS is configured to activate
> > >   this mode (e.g. policy==powersupersave).
> > >
> > >   This property is already present in the Raspian version of Linux, but the
> > >   upstream driver implementation that follows adds more details and
> > >   discerns between (a) and (b).
> > >
> > > Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
> > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > ---
> > >  Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > index 7e15aae7d69e..8b61c2179608 100644
> > > --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > @@ -64,6 +64,15 @@ properties:
> > >
> > >    aspm-no-l0s: true
> > >
> > > +  brcm,enable-l1ss:
> > > +    description: Indicates that PCIe L1SS power savings
> > > +      are desired, the downstream device is L1SS-capable, and the
> > > +      OS has been configured to enable this mode.  For boards
> >
> > What does this mean ? I don't think DT properties are supposed
> > to carry information related to how the OS is configured.
> 
> The DT setting in question is unrelated to the statement "and the OS
> has been configured to
> enable this mode".
> 
> This is merely saying that even if you enable "brcm,l1ss-enable"
> that you may not get L1SS power savings w/o setting
> "CONFIG_PCIEASPM_POWER_SUPERSAVE=y".
> I mentioned that exact term but a reviewer nakked it because
> apparently DT descriptions should not be OS specific.
> 
> I am actually open for this to be a command-line option but I wanted to honor
> what the Raspian OS folks have already done.  RaspianOS already has
> "brcm,enable-l1ss"
> set in their DTS files.

This is about the mainline kernel, I don't have any visibility into
downstream kernels (where that property management was added without DT
and PCI maintainers supervision).

Raspian OS folks' choice is theirs but it can't and it shouldn't override
the mainline review process even though I understand the position you
are in.

Thanks,
Lorenzo

> 
> Regards,
> Jim
> 
> > Again - it depends on what DT should be used for, I am not claiming to
> > have any authority on that, just asking.
> >
> > Thanks,
> > Lorenzo
> >
> > > +      using a mini-card connector, this mode may not meet the
> > > +      TCRLon maximum time of 400ns, as specified in 3.2.5.2.2
> > > +      of the PCI Express Mini CEM 2.0 specification.
> > > +    type: boolean
> > > +
> > >    brcm,scb-sizes:
> > >      description: u64 giving the 64bit PCIe memory
> > >        viewport size of a memory controller.  There may be up to
> > > --
> > > 2.17.1
> > >
> >
> >
Jim Quinlan Aug. 24, 2023, 3:19 p.m. UTC | #3 
On Wed, Aug 23, 2023 at 2:26 PM Manivannan Sadhasivam
<manivannan.sadhasivam@linaro.org> wrote:
>
> On Wed, Aug 23, 2023 at 06:29:08PM +0200, Lorenzo Pieralisi wrote:
> > On Wed, Aug 23, 2023 at 09:48:40AM -0500, Rob Herring wrote:
> > > On Wed, Aug 23, 2023 at 2:30 AM Lorenzo Pieralisi <lpieralisi@kernel.org> wrote:
> > > >
> > > > On Mon, Aug 21, 2023 at 12:01:50PM -0400, Jim Quinlan wrote:
> > > > > On Mon, Aug 21, 2023 at 11:41 AM Lorenzo Pieralisi
> > > > > <lpieralisi@kernel.org> wrote:
> > > > > >
> > > > > > On Mon, Aug 21, 2023 at 11:25:11AM -0400, Jim Quinlan wrote:
> > > > > > > On Mon, Aug 21, 2023 at 10:47 AM Lorenzo Pieralisi
> > > > > > > <lpieralisi@kernel.org> wrote:
> > > > > > > >
> > > > > > > > On Fri, Jun 23, 2023 at 10:40:54AM -0400, Jim Quinlan wrote:
> > > > > > > > > This commit adds the boolean "brcm,enable-l1ss" property:
> > > > > > > > >
> > > > > > > > >   The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs --
> > > > > > > > >   requires the driver probe() to deliberately place the HW one of three
> > > > > > > > >   CLKREQ# modes:
> > > > > > > > >
> > > > > > > > >   (a) CLKREQ# driven by the RC unconditionally
> > > > > > > > >   (b) CLKREQ# driven by the EP for ASPM L0s, L1
> > > > > > > > >   (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS).
> > > > > > > > >
> > > > > > > > >   The HW+driver can tell the difference between downstream devices that
> > > > > > > > >   need (a) and (b), but does not know when to configure (c).  All devices
> > > > > > > > >   should work fine when the driver chooses (a) or (b), but (c) may be
> > > > > > > > >   desired to realize the extra power savings that L1SS offers.  So we
> > > > > > > > >   introduce the boolean "brcm,enable-l1ss" property to inform the driver
> > > > > > > > >   that (c) is desired.  Setting this property only makes sense when the
> > > > > > > > >   downstream device is L1SS-capable and the OS is configured to activate
> > > > > > > > >   this mode (e.g. policy==powersupersave).
> > > > > > > > >
> > > > > > > > >   This property is already present in the Raspian version of Linux, but the
> > > > > > > > >   upstream driver implementation that follows adds more details and
> > > > > > > > >   discerns between (a) and (b).
> > > > > > > > >
> > > > > > > > > Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
> > > > > > > > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > > > > > > > ---
> > > > > > > > >  Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++
> > > > > > > > >  1 file changed, 9 insertions(+)
> > > > > > > > >
> > > > > > > > > diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > > > > > > > index 7e15aae7d69e..8b61c2179608 100644
> > > > > > > > > --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > > > > > > > +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > > > > > > > > @@ -64,6 +64,15 @@ properties:
> > > > > > > > >
> > > > > > > > >    aspm-no-l0s: true
> > > > > > > > >
> > > > > > > > > +  brcm,enable-l1ss:
> > > > > > > > > +    description: Indicates that PCIe L1SS power savings
> > > > > > > > > +      are desired, the downstream device is L1SS-capable, and the
> > > > > > > > > +      OS has been configured to enable this mode.  For boards
> > > > > > > >
> > > > > > > > What does this mean ? I don't think DT properties are supposed
> > > > > > > > to carry information related to how the OS is configured.
> > > > > > >
> > > > > > > The DT setting in question is unrelated to the statement "and the OS
> > > > > > > has been configured to
> > > > > > > enable this mode".
> > > > > > >
> > > > > > > This is merely saying that even if you enable "brcm,l1ss-enable"
> > > > > > > that you may not get L1SS power savings w/o setting
> > > > > > > "CONFIG_PCIEASPM_POWER_SUPERSAVE=y".
> > > > > > > I mentioned that exact term but a reviewer nakked it because
> > > > > > > apparently DT descriptions should not be OS specific.
> > >
> > > Yeah, probably the OS part should be dropped.
> >
> > I will drop it - if you don't mind.
> >
> > > > > > > I am actually open for this to be a command-line option but I wanted to honor
> > > > > > > what the Raspian OS folks have already done.  RaspianOS already has
> > > > > > > "brcm,enable-l1ss"
> > > > > > > set in their DTS files.
> > > > > >
> > > > > > This is about the mainline kernel, I don't have any visibility into
> > > > > > downstream kernels (where that property management was added without DT
> > > > > > and PCI maintainers supervision).
> > > > > >
> > > > > > Raspian OS folks' choice is theirs but it can't and it shouldn't override
> > > > > > the mainline review process even though I understand the position you
> > > > > > are in.
> > >
> > > Sure, but we shouldn't change things just to be different from
> > > downstream. If we're only discussing the color of the shed, then no
> > > point changing it.
> >
> > Sure, no problem.
> >
> > > > > Understood, but using the command line has its warts as well; I now recall the
> > > > > discussion Bjorn and I  had regarding this option.  I'm pretty sure
> > > > > that upstreaam will not allow the following
> > > > > possible command line kernel params:
> > > > >
> > > > >     brcm,enable-l1ss
> > > > >     pci=brcm,entable-l1ss
> > > > >
> > > > > Bjorn suggested using the  documented but (IMO) obscure  and  rarely
> > > > > used  format
> > > > >
> > > > >     pci=[<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*pci:<vendor>:<device>[:<subvendor>:<subdevice>]
> > > > >
> > > > > but this is just going in the wrong direction; here's why.  Using the
> > > > > above iformat s completely dependent on the
> > > > > PCI "linux-domaiin"  property,  a non-HW related DT property I  might
> > > > > add.  Since "linux-domain" is already
> > > > > a valid and well-used  DT property, and the value of  the above
> > > > > command line format is dependent
> > > > > on the value of the "linux-domain", why not be consistent and let
> > > > > "brcm,enable-l1ss" be a Broadcom specific property?
> > > >
> > > > I am just asking to add a module_param to the host controller driver.
> > >
> > > FWIW, gregkh pretty much always nacks new module parameters.
> >
> > Fine by me.
> >
> > > > Anyway - time is running out for v6.6, I need Rob's feedback, if I don't
> > > > hear from him today I will merge the last three patches and postpone the
> > > > discussion.
> > >
> > > You've already got my reviewed-by. If you aren't happy with this, then
> > > fine. I don't know enough about L1SS to comment further. Is it
> > > normally always supported or discoverable? If so, then I'd think we'd
> > > want it default enabled with a disable override flag. Maybe it should
> > > be generic?
> >
> > It is not that I am not happy with it - we asked questions to understand
> > what this property was for, I think that's normal.
> >
> > I will merge this series as-is.
> >
>
> There is a discussion ongoing here: https://lore.kernel.org/linux-pci/20230823181650.GL3737@thinkpad/T/#u
>
> Can you please hold on to merging this series until we've reached a conclusion?
 (2) There are odd boards out there which

TL;DR:  I'm okay with postponing the two clkreq# commits.

Sigh.  I really wish we had this discussion months ago when this
series was submitted.

I do think the best -- but not perfect -- way to do this is with a DT
param.  AFAICT there
is no way to do this with a command line param with it being accepted,
module_param or otherwise; please see
my reasons from this thread.  Also, Rob just said that GregH will
probably reject a new module_param
anyway.

That being said, the recent discussions are insightful and have me
reconsidering having
the "l1ss mode" be the default -- it has certainly worked well for the
RaspianOS folks.
That being said, the RaspianOS folks do not experience the flavor of
form-factors and devices
as Broadcom STB, and the admonitions of our HW designer are of great
concern to me.

In light of the above I am okay with postponing the two clkreq-related
commits to avoid any missteps.

Regards,
Jim

>
> - Mani
>
> > Lorenzo
>
> --
> மணிவண்ணன் சதாசிவம்
diff mbox series

Patch

diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
index 7e15aae7d69e..8b61c2179608 100644
--- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
+++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
@@ -64,6 +64,15 @@  properties:
 
   aspm-no-l0s: true
 
+  brcm,enable-l1ss:
+    description: Indicates that PCIe L1SS power savings
+      are desired, the downstream device is L1SS-capable, and the
+      OS has been configured to enable this mode.  For boards
+      using a mini-card connector, this mode may not meet the
+      TCRLon maximum time of 400ns, as specified in 3.2.5.2.2
+      of the PCI Express Mini CEM 2.0 specification.
+    type: boolean
+
   brcm,scb-sizes:
     description: u64 giving the 64bit PCIe memory
       viewport size of a memory controller.  There may be up to