| Message ID | 1430315508-7582-1-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 1 May 2015 at 18:18, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > On Wed, Apr 29, 2015 at 03:51:48PM +0200, Ard Biesheuvel wrote: >> This adds support for fixmap based earlycon by moving the fixmap >> initialization to an earlier stage and introducing the Kconfig symbol >> that wires up the existing code. > > I don't see the patches for this fixmap based earlycon. What's the > status of those, and how are they getting into mainline? > They are already /in/ mainline. This single patch is all that is required to wire it up for ARM. However, I did notice after sending this that another implementation had been proposed already: http://lkml.iu.edu/hypermail/linux/kernel/1412.3/00855.html I am not sure which one is more correct, but the general idea is the same, i.e., to allocate the fixmap PTEs from bss rather than the heap.
(thread is here: http://thread.gmane.org/gmane.linux.ports.arm.kernel/409329) On 2 May 2015 at 10:37, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 1 May 2015 at 18:18, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: >> On Wed, Apr 29, 2015 at 03:51:48PM +0200, Ard Biesheuvel wrote: >>> This adds support for fixmap based earlycon by moving the fixmap >>> initialization to an earlier stage and introducing the Kconfig symbol >>> that wires up the existing code. >> >> I don't see the patches for this fixmap based earlycon. What's the >> status of those, and how are they getting into mainline? >> > > They are already /in/ mainline. This single patch is all that is > required to wire it up for ARM. > > However, I did notice after sending this that another implementation > had been proposed already: > http://lkml.iu.edu/hypermail/linux/kernel/1412.3/00855.html > > I am not sure which one is more correct, but the general idea is the > same, i.e., to allocate the fixmap PTEs from bss rather than the heap. Anyone else care to comment on this? DT based earlycon is a *really* useful thing to have if you are working on early kernel code. With many of the DTs now having been extended with a /chosen/stdout-path property, it really only takes a simple 'earlycon' command line parameter (without any arguments) to get console output as soon as the early DT scan is concluded. I suppose this is also a useful thing for multi platform kernels? BTW the patch still applies to v4.1-rc6 Regards, Ard.
On 2 June 2015 at 01:31, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > On Mon, Jun 01, 2015 at 06:26:14PM -0500, Rob Herring wrote: >> On Mon, Jun 1, 2015 at 3:26 AM, Ard Biesheuvel >> <ard.biesheuvel@linaro.org> wrote: >> > (thread is here: http://thread.gmane.org/gmane.linux.ports.arm.kernel/409329) >> > >> > On 2 May 2015 at 10:37, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: >> >> On 1 May 2015 at 18:18, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: >> >>> On Wed, Apr 29, 2015 at 03:51:48PM +0200, Ard Biesheuvel wrote: >> >>>> This adds support for fixmap based earlycon by moving the fixmap >> >>>> initialization to an earlier stage and introducing the Kconfig symbol >> >>>> that wires up the existing code. >> >>> >> >>> I don't see the patches for this fixmap based earlycon. What's the >> >>> status of those, and how are they getting into mainline? >> >>> >> >> >> >> They are already /in/ mainline. This single patch is all that is >> >> required to wire it up for ARM. >> >> >> >> However, I did notice after sending this that another implementation >> >> had been proposed already: >> >> http://lkml.iu.edu/hypermail/linux/kernel/1412.3/00855.html >> >> >> >> I am not sure which one is more correct, but the general idea is the >> >> same, i.e., to allocate the fixmap PTEs from bss rather than the heap. >> > >> > Anyone else care to comment on this? >> >> You need to re-write the page table entries because the pte and pmd >> flags get adjusted during boot. For example SMP related flags get >> configured. I believe Stefan's version (based on mine which was based >> on Mark Salter's) did this. In fact, I'm surprised this works after >> paging_init, but I may have missed something. > > Any changes to PMD flags for things like SMP related flags must be > done via a remove-the-mapping, flush-tlb, add-new-mapping sequence. > OK, thanks for pointing that out. At the time I sent it, I was aware there were probably some architectural details I hadn't taken into account, and I hadn't seen Stefan's patch. So Stefan, could you please send that v2 so that we can get the ball rolling on this again? Thanks, Ard. >> > DT based earlycon is a *really* useful thing to have if you are >> > working on early kernel code. >> > With many of the DTs now having been extended with a >> > /chosen/stdout-path property, it really only takes a simple 'earlycon' >> > command line parameter (without any arguments) to get console output >> > as soon as the early DT scan is concluded. I suppose this is also a >> > useful thing for multi platform kernels? >> >> Certainly, that's the whole point. IMO, we should rip out most of >> DEBUG_LL when this is merged. > > If you think that, you're wrong. DEBUG_LL exists to be able to debug > stuff well before the kernel gets anywhere near the C code. It has > to stay. It fills the gap where no C code can do any debugging. > > -- > FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up > according to speedtest.net.
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 45df48ba0b12..0076330789f5 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -287,6 +287,9 @@ config GENERIC_BUG def_bool y depends on BUG +config FIX_EARLYCON_MEM + def_bool y + config PGTABLE_LEVELS int default 3 if ARM_LPAE diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h index 0415eae1df27..e0abd3a150ee 100644 --- a/arch/arm/include/asm/fixmap.h +++ b/arch/arm/include/asm/fixmap.h @@ -1,6 +1,10 @@ #ifndef _ASM_FIXMAP_H #define _ASM_FIXMAP_H +#include <asm/pgtable.h> + +#define FIXMAP_PAGE_IO L_PTE_PRESENT|L_PTE_YOUNG|L_PTE_DIRTY + #define FIXADDR_START 0xffc00000UL #define FIXADDR_END 0xfff00000UL #define FIXADDR_TOP (FIXADDR_END - PAGE_SIZE) @@ -11,6 +15,8 @@ enum fixed_addresses { FIX_KMAP_BEGIN, FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1, + FIX_EARLYCON_MEM_BASE, + /* Support writing RO kernel text via kprobes, jump labels, etc. */ FIX_TEXT_POKE0, FIX_TEXT_POKE1, diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index 6c777e908a24..2e4b3c22be4d 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -80,6 +80,7 @@ extern void early_paging_init(const struct machine_desc *, extern void sanity_check_meminfo(void); extern enum reboot_mode reboot_mode; extern void setup_dma_zone(const struct machine_desc *desc); +extern void early_fixmap_init(void); unsigned int processor_id; EXPORT_SYMBOL(processor_id); @@ -915,6 +916,7 @@ void __init setup_arch(char **cmdline_p) const struct machine_desc *mdesc; setup_processor(); + early_fixmap_init(); mdesc = setup_machine_fdt(__atags_pointer); if (!mdesc) mdesc = setup_machine_tags(__atags_pointer, __machine_arch_type); diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c index 4e6ef896c619..d072726c3781 100644 --- a/arch/arm/mm/mmu.c +++ b/arch/arm/mm/mmu.c @@ -1231,7 +1231,9 @@ static void __init devicemaps_init(const struct machine_desc *mdesc) early_trap_init(vectors); - for (addr = VMALLOC_START; addr; addr += PMD_SIZE) + for (addr = VMALLOC_START; addr < FIXADDR_START; addr += PMD_SIZE) + pmd_clear(pmd_off_k(addr)); + for (addr = round_up(FIXADDR_END, PMD_SIZE); addr; addr += PMD_SIZE) pmd_clear(pmd_off_k(addr)); /* @@ -1321,9 +1323,17 @@ static void __init kmap_init(void) pkmap_page_table = early_pte_alloc(pmd_off_k(PKMAP_BASE), PKMAP_BASE, _PAGE_KERNEL_TABLE); #endif +} + +void __init early_fixmap_init(void) +{ + static u8 fixmap_pte[PTE_HWTABLE_OFF + PTE_HWTABLE_SIZE] __page_aligned_bss; + pmd_t *pmd = pmd_off_k(FIXADDR_START); + + if (pmd_none(*pmd)) + __pmd_populate(pmd, __pa(fixmap_pte), _PAGE_KERNEL_TABLE); - early_pte_alloc(pmd_off_k(FIXADDR_START), FIXADDR_START, - _PAGE_KERNEL_TABLE); + BUG_ON(pmd_bad(*pmd)); } static void __init map_lowmem(void)
This adds support for fixmap based earlycon by moving the fixmap initialization to an earlier stage and introducing the Kconfig symbol that wires up the existing code. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm/Kconfig | 3 +++ arch/arm/include/asm/fixmap.h | 6 ++++++ arch/arm/kernel/setup.c | 2 ++ arch/arm/mm/mmu.c | 16 +++++++++++++--- 4 files changed, 24 insertions(+), 3 deletions(-)