[Intel-gfx] [PATCH] drm/i915: Perf_limit_reasons are only available for Gen11+

[Rodrigo Vivi]

On Wed, Sep 28, 2022 at 11:17:06AM -0700, Dixit, Ashutosh wrote:
> On Wed, 28 Sep 2022 04:38:46 -0700, Jani Nikula wrote:
> >
> > On Mon, 19 Sep 2022, Ashutosh Dixit <ashutosh.dixit at intel.com> wrote:
> > > Register GT0_PERF_LIMIT_REASONS (0x1381a8) is available only for
> > > Gen11+. Therefore ensure perf_limit_reasons sysfs/debugfs files are created
> > > only for Gen11+. Otherwise on Gen < 5 accessing these files results in the
> > > following oops:
> > >
> > > <1> [88.829420] BUG: unable to handle page fault for address: ffffc90000bb81a8
> > > <1> [88.829438] #PF: supervisor read access in kernel mode
> > > <1> [88.829447] #PF: error_code(0x0000) - not-present page
> > >
> > > Bspec: 20008
> > > Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/6863
> > > Fixes: fe5979665f64 ("drm/i915/debugfs: Add perf_limit_reasons in debugfs")
> > > Fixes: fa68bff7cf27 ("drm/i915/gt: Add sysfs throttle frequency interfaces")
> > > Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
> >
> 
> Hi Jani,
> 
> > Ashutosh, can you provide a backport of this i.e. commit 0d2d201095e9
> > ("drm/i915: Perf_limit_reasons are only available for Gen11+") that
> > applies cleanly on drm-intel-fixes, please?
> 
> I've sent the patch:
> 
> https://patchwork.freedesktop.org/series/109196/
> 
> Not sure though if it is worth applying on drm-intel-fixes because of one
> conflict with drm-tip which will need to be resolved manually. On

The conflict shouldn't be that bad to resolve, but since the patch deviates
from the original, the new commit message needs to highlight and explain
that this is a backport and the reasons of the difference and including the sha
of the already merged patch. Similar to the option 3 of the stable rules. [1].

Well, another option is to wait until this patch gets propagated to Linus master
and then send the backported version to the stable mailing list. But again,
with the proper rules of the option 3. [1]

[1] - https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

> drm-intel-fixes the crash mentioned above will be seen only on Gen < 5 if
> someone manually cat's the sysfs. We had to fix on drm-tip because there
> was a CI failure with Gen3 debugfs but that code is not in drm-intel-fixes.

since it is sysfs it is probably a good protection to have anyway.

> 
> Thanks.
> --
> Ashutosh