[PATCH 0/1] Fix DRM driver initialization failure in kernel v5.14

[PATCH 0/1] Fix DRM driver initialization failure in kernel v5.14

[Dan Moulding]

After trying out kernel v5.14-rc5 on my system, I no longer get any
display output. Checking dmesg, I found it's because my DRM driver
(nouveau) is failing at ttm_device_init. That is failing because of a
behavior change in ttm_global_init with respect to debugfs. debugfs is
disabled on my system, which causes ttm_global_init to fail. The
following patch fixes the issue by ignoring the debugfs failure, which
is expected, rather than allowing it to cause ttm_global_init to fail.

Dan Moulding (1):
  drm: ttm: Don't bail from ttm_global_init if debugfs_create_dir fails

 drivers/gpu/drm/ttm/ttm_device.c | 2 --
 1 file changed, 2 deletions(-)

-- 
2.31.1

[PATCH 1/1] drm: ttm: Don't bail from ttm_global_init if debugfs_create_dir fails

[Dan Moulding]

In 69de4421bb4c ("drm/ttm: Initialize debugfs from
ttm_global_init()"), ttm_global_init was changed so that if creation
of the debugfs global root directory fails, ttm_global_init will bail
out early and return an error, leading to initialization failure of
DRM drivers. However, not every system will be using debugfs. On such
a system, debugfs directory creation can be expected to fail, but DRM
drivers must still be usable. This changes it so that if creation of
TTM's debugfs root directory fails, then no biggie: keep calm and
carry on.

Fixes: 69de4421bb4c ("drm/ttm: Initialize debugfs from ttm_global_init()")
Signed-off-by: Dan Moulding <dmoulding@me.com>
---
 drivers/gpu/drm/ttm/ttm_device.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
index 74e3b460132b..2df59b3c2ea1 100644
--- a/drivers/gpu/drm/ttm/ttm_device.c
+++ b/drivers/gpu/drm/ttm/ttm_device.c
@@ -78,9 +78,7 @@ static int ttm_global_init(void)
 
 	ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
 	if (IS_ERR(ttm_debugfs_root)) {
-		ret = PTR_ERR(ttm_debugfs_root);
 		ttm_debugfs_root = NULL;
-		goto out;
 	}
 
 	/* Limit the number of pages in the pool to about 50% of the total
-- 
2.31.1

Re: [PATCH 1/1] drm: ttm: Don't bail from ttm_global_init if debugfs_create_dir fails

[Huacai Chen]

Tested-by: Huacai Chen <chenhuacai@loongson.cn>

On Wed, Aug 11, 2021 at 6:42 AM Dan Moulding <dmoulding@me.com> wrote:
>
> In 69de4421bb4c ("drm/ttm: Initialize debugfs from
> ttm_global_init()"), ttm_global_init was changed so that if creation
> of the debugfs global root directory fails, ttm_global_init will bail
> out early and return an error, leading to initialization failure of
> DRM drivers. However, not every system will be using debugfs. On such
> a system, debugfs directory creation can be expected to fail, but DRM
> drivers must still be usable. This changes it so that if creation of
> TTM's debugfs root directory fails, then no biggie: keep calm and
> carry on.
>
> Fixes: 69de4421bb4c ("drm/ttm: Initialize debugfs from ttm_global_init()")
> Signed-off-by: Dan Moulding <dmoulding@me.com>
> ---
>  drivers/gpu/drm/ttm/ttm_device.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 74e3b460132b..2df59b3c2ea1 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -78,9 +78,7 @@ static int ttm_global_init(void)
>
>         ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
>         if (IS_ERR(ttm_debugfs_root)) {
> -               ret = PTR_ERR(ttm_debugfs_root);
>                 ttm_debugfs_root = NULL;
> -               goto out;
>         }
>
>         /* Limit the number of pages in the pool to about 50% of the total
> --
> 2.31.1
>

Re: [PATCH 0/1] Fix DRM driver initialization failure in kernel v5.14

[Dan Moulding]

Just a friendly reminder that this fix for a regression needs
review. It should be a quick review.

It would probably be good to ensure this gets in before the final 5.14
release, otherwise this is going to be a very visible regression for
anyone that uses DRM and does not use debugfs.

Thanks!

-- Dan

Re: [PATCH 1/1] drm: ttm: Don't bail from ttm_global_init if debugfs_create_dir fails

[Huang Rui]

On Wed, Aug 11, 2021 at 03:59:06AM +0800, Dan Moulding wrote:
> In 69de4421bb4c ("drm/ttm: Initialize debugfs from
> ttm_global_init()"), ttm_global_init was changed so that if creation
> of the debugfs global root directory fails, ttm_global_init will bail
> out early and return an error, leading to initialization failure of
> DRM drivers. However, not every system will be using debugfs. On such
> a system, debugfs directory creation can be expected to fail, but DRM
> drivers must still be usable. This changes it so that if creation of
> TTM's debugfs root directory fails, then no biggie: keep calm and
> carry on.
> 
> Fixes: 69de4421bb4c ("drm/ttm: Initialize debugfs from ttm_global_init()")
> Signed-off-by: Dan Moulding <dmoulding@me.com>

It looks ok for me.

Reviewed-by: Huang Rui <ray.huang@amd.com>

Thanks,
Ray

> ---
>  drivers/gpu/drm/ttm/ttm_device.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 74e3b460132b..2df59b3c2ea1 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -78,9 +78,7 @@ static int ttm_global_init(void)
>  
>  	ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
>  	if (IS_ERR(ttm_debugfs_root)) {
> -		ret = PTR_ERR(ttm_debugfs_root);
>  		ttm_debugfs_root = NULL;
> -		goto out;
>  	}
>  
>  	/* Limit the number of pages in the pool to about 50% of the total
> -- 
> 2.31.1
> 

Re: [PATCH 0/1] Fix DRM driver initialization failure in kernel v5.14

[Huang Rui]

On Sat, Aug 14, 2021 at 12:50:14AM +0800, Dan Moulding wrote:
> Just a friendly reminder that this fix for a regression needs
> review. It should be a quick review.
> 
> It would probably be good to ensure this gets in before the final 5.14
> release, otherwise this is going to be a very visible regression for
> anyone that uses DRM and does not use debugfs.
> 

Just took a look at your patch, it's ok for me. Alex/Christian, could you
help to apply this fix if you have no concern?

Best Regards,
Ray

Re: [PATCH 1/1] drm: ttm: Don't bail from ttm_global_init if debugfs_create_dir fails

[Christian König]

Am 10.08.21 um 21:59 schrieb Dan Moulding:
> In 69de4421bb4c ("drm/ttm: Initialize debugfs from
> ttm_global_init()"), ttm_global_init was changed so that if creation
> of the debugfs global root directory fails, ttm_global_init will bail
> out early and return an error, leading to initialization failure of
> DRM drivers. However, not every system will be using debugfs. On such
> a system, debugfs directory creation can be expected to fail, but DRM
> drivers must still be usable. This changes it so that if creation of
> TTM's debugfs root directory fails, then no biggie: keep calm and
> carry on.
>
> Fixes: 69de4421bb4c ("drm/ttm: Initialize debugfs from ttm_global_init()")
> Signed-off-by: Dan Moulding <dmoulding@me.com>

Good point, patch is Reviewed-by: Christian König 
<christian.koenig@amd.com>.

Going to pick that up later today.

Regards,
Christian.

> ---
>   drivers/gpu/drm/ttm/ttm_device.c | 2 --
>   1 file changed, 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 74e3b460132b..2df59b3c2ea1 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -78,9 +78,7 @@ static int ttm_global_init(void)
>   
>   	ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
>   	if (IS_ERR(ttm_debugfs_root)) {
> -		ret = PTR_ERR(ttm_debugfs_root);
>   		ttm_debugfs_root = NULL;
> -		goto out;
>   	}
>   
>   	/* Limit the number of pages in the pool to about 50% of the total

Re: [PATCH 0/1] Fix DRM driver initialization failure in kernel v5.14

[Christian König]

Am 16.08.21 um 08:20 schrieb Huang Rui:
> On Sat, Aug 14, 2021 at 12:50:14AM +0800, Dan Moulding wrote:
>> Just a friendly reminder that this fix for a regression needs
>> review. It should be a quick review.
>>
>> It would probably be good to ensure this gets in before the final 5.14
>> release, otherwise this is going to be a very visible regression for
>> anyone that uses DRM and does not use debugfs.
>>
> Just took a look at your patch, it's ok for me. Alex/Christian, could you
> help to apply this fix if you have no concern?

Sorry for the delay, just came back from vacation today.

Patch is pushed to drm-misc-fixes and will hopefully still get into 5.14.

Thanks,
Christian.

>
> Best Regards,
> Ray

Re: [PATCH 1/1] drm: ttm: Don't bail from ttm_global_init if debugfs_create_dir fails

[Jason Ekstrand]

Makes sense

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

On Mon, Aug 16, 2021 at 2:40 AM Christian König
<christian.koenig@amd.com> wrote:
>
> Am 10.08.21 um 21:59 schrieb Dan Moulding:
> > In 69de4421bb4c ("drm/ttm: Initialize debugfs from
> > ttm_global_init()"), ttm_global_init was changed so that if creation
> > of the debugfs global root directory fails, ttm_global_init will bail
> > out early and return an error, leading to initialization failure of
> > DRM drivers. However, not every system will be using debugfs. On such
> > a system, debugfs directory creation can be expected to fail, but DRM
> > drivers must still be usable. This changes it so that if creation of
> > TTM's debugfs root directory fails, then no biggie: keep calm and
> > carry on.
> >
> > Fixes: 69de4421bb4c ("drm/ttm: Initialize debugfs from ttm_global_init()")
> > Signed-off-by: Dan Moulding <dmoulding@me.com>
>
> Good point, patch is Reviewed-by: Christian König
> <christian.koenig@amd.com>.
>
> Going to pick that up later today.
>
> Regards,
> Christian.
>
> > ---
> >   drivers/gpu/drm/ttm/ttm_device.c | 2 --
> >   1 file changed, 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> > index 74e3b460132b..2df59b3c2ea1 100644
> > --- a/drivers/gpu/drm/ttm/ttm_device.c
> > +++ b/drivers/gpu/drm/ttm/ttm_device.c
> > @@ -78,9 +78,7 @@ static int ttm_global_init(void)
> >
> >       ttm_debugfs_root = debugfs_create_dir("ttm", NULL);
> >       if (IS_ERR(ttm_debugfs_root)) {
> > -             ret = PTR_ERR(ttm_debugfs_root);
> >               ttm_debugfs_root = NULL;
> > -             goto out;
> >       }
> >
> >       /* Limit the number of pages in the pool to about 50% of the total
>