[v3,0/3] Add interconnect debugfs client

This series introduces interconnect debugfs files that support voting
for any path the framework supports.

We've historically relied on an out-of-tree module for this, which used
the old icc_get() that was recently removed in [0]. The old icc_get()
took integer endpoint IDs, which made identifying paths in our old
implementation non-intuitive. The logical node names typically don't
change much chip-to-chip, but the raw integer IDs do. Take this
opportunity to introduce an icc_get() that uses string names instead,
which allows for a more intuitive and generic debugfs interface.

We rely on this support for debug, test, and verification. Hopefully
it'll be useful for other vendors as well.

[0] commit 7dcdad6f32c9 ("interconnect: drop unused icc_get() interface")

Changes in v3:
- Use GFP_ATOMIC when allocating with the rcu lock held.

Changes in v2:
- Make icc_get() an internal interface.
- RCU-protect src_node and dst_node.
- Replace PLATFORM_DEVID_AUTO with PLATFORM_DEVID_NONE.
- Remove unnecessary #include.
- Add debugfs client documentation.

Mike Tipton (3):
  debugfs: Add write support to debugfs_create_str()
  interconnect: Reintroduce icc_get()
  interconnect: Add debugfs test client

 Documentation/driver-api/interconnect.rst |  25 ++++
 drivers/interconnect/Makefile             |   2 +-
 drivers/interconnect/core.c               |  66 +++++++++
 drivers/interconnect/debugfs-client.c     | 168 ++++++++++++++++++++++
 drivers/interconnect/internal.h           |   3 +
 fs/debugfs/file.c                         |  48 ++++++-
 6 files changed, 309 insertions(+), 3 deletions(-)
 create mode 100644 drivers/interconnect/debugfs-client.c

On 7.08.23 17:29, Mike Tipton wrote:
> Currently, debugfs_create_str() only supports reading strings from
> debugfs. Add support for writing them as well.
> 
> Based on original implementation by Peter Zijlstra [0]. Write support
> was present in the initial patch version, but dropped in v2 due to lack
> of users. We have a user now, so reintroduce it.
> 
> [0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@hirez.programming.kicks-ass.net/
> 

Hi Greg,

Looks like the original code was reviewed two years ago (not sure if it
counts). But in any case, i need an ack from you to apply this.

There is no build dependency with the rest of the patches (but there is a
functional one). It should be also fine if you apply it directly, if you
prefer so?

Thanks,
Georgi

> Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
> ---
>   fs/debugfs/file.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 46 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index b7711888dd17..87b3753aa4b1 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -904,8 +904,52 @@ EXPORT_SYMBOL_GPL(debugfs_create_str);
>   static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,
>   				      size_t count, loff_t *ppos)
>   {
> -	/* This is really only for read-only strings */
> -	return -EINVAL;
> +	struct dentry *dentry = F_DENTRY(file);
> +	char *old, *new = NULL;
> +	int pos = *ppos;
> +	int r;
> +
> +	r = debugfs_file_get(dentry);
> +	if (unlikely(r))
> +		return r;
> +
> +	old = *(char **)file->private_data;
> +
> +	/* only allow strict concatenation */
> +	r = -EINVAL;
> +	if (pos && pos != strlen(old))
> +		goto error;
> +
> +	r = -E2BIG;
> +	if (pos + count + 1 > PAGE_SIZE)
> +		goto error;
> +
> +	r = -ENOMEM;
> +	new = kmalloc(pos + count + 1, GFP_KERNEL);
> +	if (!new)
> +		goto error;
> +
> +	if (pos)
> +		memcpy(new, old, pos);
> +
> +	r = -EFAULT;
> +	if (copy_from_user(new + pos, user_buf, count))
> +		goto error;
> +
> +	new[pos + count] = '\0';
> +	strim(new);
> +
> +	rcu_assign_pointer(*(char **)file->private_data, new);
> +	synchronize_rcu();
> +	kfree(old);
> +
> +	debugfs_file_put(dentry);
> +	return count;
> +
> +error:
> +	kfree(new);
> +	debugfs_file_put(dentry);
> +	return r;
>   }
>   
>   static const struct file_operations fops_str = {

On Sat, Aug 12, 2023 at 12:36:12PM +0200, Greg KH wrote:
> On Fri, Aug 11, 2023 at 10:46:34AM +0300, Georgi Djakov wrote:
> > On 7.08.23 17:29, Mike Tipton wrote:
> > > Currently, debugfs_create_str() only supports reading strings from
> > > debugfs. Add support for writing them as well.
> > > 
> > > Based on original implementation by Peter Zijlstra [0]. Write support
> > > was present in the initial patch version, but dropped in v2 due to lack
> > > of users. We have a user now, so reintroduce it.
> > > 
> > > [0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@hirez.programming.kicks-ass.net/
> > > 
> > 
> > Hi Greg,
> > 
> > Looks like the original code was reviewed two years ago (not sure if it
> > counts). But in any case, i need an ack from you to apply this.
> > 
> > There is no build dependency with the rest of the patches (but there is a
> > functional one). It should be also fine if you apply it directly, if you
> > prefer so?
> 
> Feel free for this to go with the code that uses it:
> 
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Wait, no, this isn't ok, this ACK is now rescinded:

NACKED-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Hi Greg,

Thanks for the comments!

On 12.08.23 13:40, Greg KH wrote:
> On Mon, Aug 07, 2023 at 07:29:12AM -0700, Mike Tipton wrote:
>> Currently, debugfs_create_str() only supports reading strings from
>> debugfs. Add support for writing them as well.
>>
>> Based on original implementation by Peter Zijlstra [0]. Write support
>> was present in the initial patch version, but dropped in v2 due to lack
>> of users. We have a user now, so reintroduce it.
>>
>> [0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@hirez.programming.kicks-ass.net/
>>
>> Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
>> ---
>>   fs/debugfs/file.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 46 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>> index b7711888dd17..87b3753aa4b1 100644
>> --- a/fs/debugfs/file.c
>> +++ b/fs/debugfs/file.c
>> @@ -904,8 +904,52 @@ EXPORT_SYMBOL_GPL(debugfs_create_str);
>>   static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,
>>   				      size_t count, loff_t *ppos)
>>   {
>> -	/* This is really only for read-only strings */
>> -	return -EINVAL;
>> +	struct dentry *dentry = F_DENTRY(file);
>> +	char *old, *new = NULL;
>> +	int pos = *ppos;
>> +	int r;
>> +
>> +	r = debugfs_file_get(dentry);
>> +	if (unlikely(r))
>> +		return r;
>> +
>> +	old = *(char **)file->private_data;
>> +
>> +	/* only allow strict concatenation */
>> +	r = -EINVAL;
>> +	if (pos && pos != strlen(old))
>> +		goto error;
>> +
>> +	r = -E2BIG;
>> +	if (pos + count + 1 > PAGE_SIZE)
>> +		goto error;
>> +
>> +	r = -ENOMEM;
>> +	new = kmalloc(pos + count + 1, GFP_KERNEL);
>> +	if (!new)
>> +		goto error;
>> +
>> +	if (pos)
>> +		memcpy(new, old, pos);
>> +
>> +	r = -EFAULT;
>> +	if (copy_from_user(new + pos, user_buf, count))
>> +		goto error;
>> +
>> +	new[pos + count] = '\0';
>> +	strim(new);
>> +
>> +	rcu_assign_pointer(*(char **)file->private_data, new);
>> +	synchronize_rcu();
>> +	kfree(old);
>> +
>> +	debugfs_file_put(dentry);
>> +	return count;
>> +
>> +error:
>> +	kfree(new);
>> +	debugfs_file_put(dentry);
>> +	return r;
>>   }
> 
> So you just added write support for ALL debugfs files that use the
> string interface, what did you just allow to break?

Not really. According to the existing code, the write support for strings
is enabled only when the file is created with +w permissions. For read-only
files, we use fops_str_ro, which is the case for all existing string files:

$ git grep -w debugfs_create_str | egrep -v "fs/debugfs/file.c|include/linux/debugfs.h"
drivers/firmware/arm_scmi/driver.c:	debugfs_create_str("instance_name", 0400, top_dentry,
drivers/firmware/arm_scmi/driver.c:	debugfs_create_str("type", 0400, trans, (char **)&dbg->type);
drivers/opp/debugfs.c:	debugfs_create_str("of_name", S_IRUGO, d, (char **)&opp->of_name);

For fops_str_ro, the .write function is not implemented, so nothing should break?

> I recommend just using your own debugfs file function instead, as this
> could cause bad problems, right?

Agree, and that should be exactly what this patch does.

> Are you sure that all string calls can
> handle the variable be freed underneath it like this call will allow to
> happen?

Looks fine, at least for this patch-set.

Thanks,
Georgi

Hi Greg,

On 12.08.23 13:40, Greg KH wrote:
> On Mon, Aug 07, 2023 at 07:29:12AM -0700, Mike Tipton wrote:
>> Currently, debugfs_create_str() only supports reading strings from
>> debugfs. Add support for writing them as well.
>>
>> Based on original implementation by Peter Zijlstra [0]. Write support
>> was present in the initial patch version, but dropped in v2 due to lack
>> of users. We have a user now, so reintroduce it.
>>
>> [0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@hirez.programming.kicks-ass.net/
>>
>> Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
>> ---
>>   fs/debugfs/file.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 46 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>> index b7711888dd17..87b3753aa4b1 100644
>> --- a/fs/debugfs/file.c
>> +++ b/fs/debugfs/file.c
>> @@ -904,8 +904,52 @@ EXPORT_SYMBOL_GPL(debugfs_create_str);
>>   static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,
>>   				      size_t count, loff_t *ppos)
>>   {
>> -	/* This is really only for read-only strings */
>> -	return -EINVAL;
>> +	struct dentry *dentry = F_DENTRY(file);
>> +	char *old, *new = NULL;
>> +	int pos = *ppos;
>> +	int r;
>> +
>> +	r = debugfs_file_get(dentry);
>> +	if (unlikely(r))
>> +		return r;
>> +
>> +	old = *(char **)file->private_data;
>> +
>> +	/* only allow strict concatenation */
>> +	r = -EINVAL;
>> +	if (pos && pos != strlen(old))
>> +		goto error;
>> +
>> +	r = -E2BIG;
>> +	if (pos + count + 1 > PAGE_SIZE)
>> +		goto error;
>> +
>> +	r = -ENOMEM;
>> +	new = kmalloc(pos + count + 1, GFP_KERNEL);
>> +	if (!new)
>> +		goto error;
>> +
>> +	if (pos)
>> +		memcpy(new, old, pos);
>> +
>> +	r = -EFAULT;
>> +	if (copy_from_user(new + pos, user_buf, count))
>> +		goto error;
>> +
>> +	new[pos + count] = '\0';
>> +	strim(new);
>> +
>> +	rcu_assign_pointer(*(char **)file->private_data, new);
>> +	synchronize_rcu();
>> +	kfree(old);
>> +
>> +	debugfs_file_put(dentry);
>> +	return count;
>> +
>> +error:
>> +	kfree(new);
>> +	debugfs_file_put(dentry);
>> +	return r;
>>   }
> 
> So you just added write support for ALL debugfs files that use the
> string interface, what did you just allow to break?

Not true. Write support is added only for debugfs string files that are
created with +w permissions. All existing files are created as read-only
and use the fops_str_ro ops.

> I recommend just using your own debugfs file function instead, as this
> could cause bad problems, right?  Are you sure that all string calls can
> handle the variable be freed underneath it like this call will allow to
> happen?
> 
> So I wouldn't recommend doing this, sorry.
> 

Maybe you missed the fact that the different file ops are already there
and are selected based on permissions:

> static const struct file_operations fops_str = {
>         .read =         debugfs_read_file_str,
>         .write =        debugfs_write_file_str,
>         .open =         simple_open,
>         .llseek =       default_llseek,
> };
> 
> static const struct file_operations fops_str_ro = {
>         .read =         debugfs_read_file_str,
>         .open =         simple_open,
>         .llseek =       default_llseek,
> };
> 
> static const struct file_operations fops_str_wo = {
>         .write =        debugfs_write_file_str,
>         .open =         simple_open,
>         .llseek =       default_llseek,
> };

...so this patch is doing exactly what you suggested? If you agree,
could you ack it again please?

Thanks,
Georgi

On Fri, Aug 18, 2023 at 01:05:57PM +0300, Georgi Djakov wrote:
> Hi Greg,
> 
> On 12.08.23 13:40, Greg KH wrote:
> > On Mon, Aug 07, 2023 at 07:29:12AM -0700, Mike Tipton wrote:
> > > Currently, debugfs_create_str() only supports reading strings from
> > > debugfs. Add support for writing them as well.
> > > 
> > > Based on original implementation by Peter Zijlstra [0]. Write support
> > > was present in the initial patch version, but dropped in v2 due to lack
> > > of users. We have a user now, so reintroduce it.
> > > 
> > > [0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@hirez.programming.kicks-ass.net/
> > > 
> > > Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
> > > ---
> > >   fs/debugfs/file.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--
> > >   1 file changed, 46 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> > > index b7711888dd17..87b3753aa4b1 100644
> > > --- a/fs/debugfs/file.c
> > > +++ b/fs/debugfs/file.c
> > > @@ -904,8 +904,52 @@ EXPORT_SYMBOL_GPL(debugfs_create_str);
> > >   static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,
> > >   				      size_t count, loff_t *ppos)
> > >   {
> > > -	/* This is really only for read-only strings */
> > > -	return -EINVAL;
> > > +	struct dentry *dentry = F_DENTRY(file);
> > > +	char *old, *new = NULL;
> > > +	int pos = *ppos;
> > > +	int r;
> > > +
> > > +	r = debugfs_file_get(dentry);
> > > +	if (unlikely(r))
> > > +		return r;
> > > +
> > > +	old = *(char **)file->private_data;
> > > +
> > > +	/* only allow strict concatenation */
> > > +	r = -EINVAL;
> > > +	if (pos && pos != strlen(old))
> > > +		goto error;
> > > +
> > > +	r = -E2BIG;
> > > +	if (pos + count + 1 > PAGE_SIZE)
> > > +		goto error;
> > > +
> > > +	r = -ENOMEM;
> > > +	new = kmalloc(pos + count + 1, GFP_KERNEL);
> > > +	if (!new)
> > > +		goto error;
> > > +
> > > +	if (pos)
> > > +		memcpy(new, old, pos);
> > > +
> > > +	r = -EFAULT;
> > > +	if (copy_from_user(new + pos, user_buf, count))
> > > +		goto error;
> > > +
> > > +	new[pos + count] = '\0';
> > > +	strim(new);
> > > +
> > > +	rcu_assign_pointer(*(char **)file->private_data, new);
> > > +	synchronize_rcu();
> > > +	kfree(old);
> > > +
> > > +	debugfs_file_put(dentry);
> > > +	return count;
> > > +
> > > +error:
> > > +	kfree(new);
> > > +	debugfs_file_put(dentry);
> > > +	return r;
> > >   }
> > 
> > So you just added write support for ALL debugfs files that use the
> > string interface, what did you just allow to break?
> 
> Not true. Write support is added only for debugfs string files that are
> created with +w permissions. All existing files are created as read-only
> and use the fops_str_ro ops.
> 
> > I recommend just using your own debugfs file function instead, as this
> > could cause bad problems, right?  Are you sure that all string calls can
> > handle the variable be freed underneath it like this call will allow to
> > happen?
> > 
> > So I wouldn't recommend doing this, sorry.
> > 
> 
> Maybe you missed the fact that the different file ops are already there
> and are selected based on permissions:
> 
> > static const struct file_operations fops_str = {
> >         .read =         debugfs_read_file_str,
> >         .write =        debugfs_write_file_str,
> >         .open =         simple_open,
> >         .llseek =       default_llseek,
> > };
> > 
> > static const struct file_operations fops_str_ro = {
> >         .read =         debugfs_read_file_str,
> >         .open =         simple_open,
> >         .llseek =       default_llseek,
> > };
> > 
> > static const struct file_operations fops_str_wo = {
> >         .write =        debugfs_write_file_str,
> >         .open =         simple_open,
> >         .llseek =       default_llseek,
> > };
> 
> ...so this patch is doing exactly what you suggested? If you agree,
> could you ack it again please?

Yes, I did miss that, sorry, my appologies for dragging this out so
long:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>