Re: [PATCH] drm/msm/a6xx: fix for kernels without CONFIG_NVMEM

[Akhil P Oommen]

On 2/18/2021 9:41 PM, Rob Clark wrote:
> On Thu, Feb 18, 2021 at 4:28 AM Akhil P Oommen <akhilpo@xxxxxxxxxxxxxx> wrote:
> > On 2/18/2021 2:05 AM, Jonathan Marek wrote:
> > > On 2/17/21 3:18 PM, Rob Clark wrote:
> > > > On Wed, Feb 17, 2021 at 11:08 AM Jordan Crouse
> > > > <jcrouse@xxxxxxxxxxxxxx> wrote:
> > > > > On Wed, Feb 17, 2021 at 07:14:16PM +0530, Akhil P Oommen wrote:
> > > > > > On 2/17/2021 8:36 AM, Rob Clark wrote:
> > > > > > > On Tue, Feb 16, 2021 at 12:10 PM Jonathan Marek <jonathan@xxxxxxxx>
> > > > > > > wrote:
> > > > > > > > Ignore nvmem_cell_get() EOPNOTSUPP error in the same way as a
> > > > > > > > ENOENT error,
> > > > > > > > to fix the case where the kernel was compiled without CONFIG_NVMEM.
> > > > > > > >
> > > > > > > > Fixes: fe7952c629da ("drm/msm: Add speed-bin support to a618 gpu")
> > > > > > > > Signed-off-by: Jonathan Marek <jonathan@xxxxxxxx>
> > > > > > > > ---
> > > > > > > >    drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 6 +++---
> > > > > > > >    1 file changed, 3 insertions(+), 3 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > > > > > > b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > > > > > > index ba8e9d3cf0fe..7fe5d97606aa 100644
> > > > > > > > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > > > > > > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > > > > > > > @@ -1356,10 +1356,10 @@ static int a6xx_set_supported_hw(struct
> > > > > > > > device *dev, struct a6xx_gpu *a6xx_gpu,
> > > > > > > >
> > > > > > > >           cell = nvmem_cell_get(dev, "speed_bin");
> > > > > > > >           /*
> > > > > > > > -        * -ENOENT means that the platform doesn't support
> > > > > > > > speedbin which is
> > > > > > > > -        * fine
> > > > > > > > +        * -ENOENT means no speed bin in device tree,
> > > > > > > > +        * -EOPNOTSUPP means kernel was built without CONFIG_NVMEM
> > > > > > >
> > > > > > > very minor nit, it would be nice to at least preserve the gist of the
> > > > > > > "which is fine" (ie. some variation of "this is an optional thing and
> > > > > > > things won't catch fire without it" ;-))
> > > > > > >
> > > > > > > (which is, I believe, is true, hopefully Akhil could confirm.. if not
> > > > > > > we should have a harder dependency on CONFIG_NVMEM..)
> > > > > > IIRC, if the gpu opp table in the DT uses the 'opp-supported-hw'
> > > > > > property,
> > > > > > we will see some error during boot up if we don't call
> > > > > > dev_pm_opp_set_supported_hw(). So calling "nvmem_cell_get(dev,
> > > > > > "speed_bin")"
> > > > > > is a way to test this.
> > > > > >
> > > > > > If there is no other harm, we can put a hard dependency on
> > > > > > CONFIG_NVMEM.
> > > > >
> > > > > I'm not sure if we want to go this far given the squishiness about
> > > > > module
> > > > > dependencies. As far as I know we are the only driver that uses this
> > > > > seriously
> > > > > on QCOM SoCs and this is only needed for certain targets. I don't
> > > > > know if we
> > > > > want to force every target to build NVMEM and QFPROM on our behalf.
> > > > > But maybe
> > > > > I'm just saying that because Kconfig dependencies tend to break my
> > > > > brain (and
> > > > > then Arnd has to send a patch to fix it).
> > > >
> > > > Hmm, good point.. looks like CONFIG_NVMEM itself doesn't have any
> > > > other dependencies, so I suppose it wouldn't be the end of the world
> > > > to select that.. but I guess we don't want to require QFPROM
> > > >
> > > > I guess at the end of the day, what is the failure mode if you have a
> > > > speed-bin device, but your kernel config misses QFPROM (and possibly
> > > > NVMEM)?  If the result is just not having the highest clk rate(s)
> >
> > Atleast on sc7180's gpu, using an unsupported FMAX breaks gmu. It won't
> > be very obvious what went wrong when this happens!
>
> Ugg, ok..
>
> I suppose we could select NVMEM, but not QFPROM, and then the case
> where QFPROM is not enabled on platforms that have the speed-bin field
> in DT will fail gracefully and all other platforms would continue on
> happily?
>
> BR,
> -R

Sounds good to me.

-Akhil.

> > > > available, that isn't the end of the world.  But if it makes things
> > > > not-work, that is sub-optimal.  Generally, especially on ARM, kconfig
> > > > seems to be way harder than it should be to build a kernel that works,
> > > > if we could somehow not add to that problem (for both people with a6xx
> > > > and older gens) that would be nice ;-)
> > >
> > > There is a "imply" kconfig option which solves exactly this problem.
> > > (you would "imply NVMEM" instead of "select NVMEM". then it would be
> > > possible to disable NVMEM but it would get enabled by default)
> > >
> > > > BR,
> > > > -R
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