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

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Wed, 28 Sep 2022 11:35:18 -0700, Rodrigo Vivi wrote:
>
> 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@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@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

Hi Rodrigo,

> 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].

I have improved the commit message and sent out a v2. Please take a look.

Thanks.
--
Ashutosh

> 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