Re: [Freedreno] [PATCH] drm/msm: Only enable A6xx LLCC code on A6xx

[Sai Prakash Ranjan]

Hi Rob,

On 2021-01-08 22:16, Rob Clark wrote:
> On Fri, Jan 8, 2021 at 6:05 AM Sai Prakash Ranjan
> <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
> > On 2021-01-08 19:09, Konrad Dybcio wrote:
> > >> Konrad, can you please test this below change without your change?
> > >
> > > This brings no difference, a BUG still happens. We're still calling
> > > to_a6xx_gpu on ANY device that's probed! Too bad it won't turn my A330
> > > into an A640..
> > >
> > > Also, relying on disabling LLCC in the config is out of question as it
> > > makes the arm32 kernel not compile with DRM/MSM and it just removes
> > > the functionality on devices with a6xx.. (unless somebody removes the
> > > dependency on it, which in my opinion is even worse and will cause
> > > more problems for developers!).
> > >
> >
> > Disabling LLCC is not the suggestion, I was under the impression that
> > was the cause here for the smmu bug. Anyways, the check for llc slice
> > in case llcc is disabled is not correct as well. I will send a patch 
> > for
> > that as well.
> >
> > > The bigger question is how and why did that piece of code ever make it
> > > to adreno_gpu.c and not a6xx_gpu.c?
> > >
> >
> > My mistake, I will move it.
>
> Thanks, since we don't have kernel-CI coverage for gpu, and there
> probably isn't one person who has all the different devices supported
> (or enough hours in the day to test them all), it is probably
> better/safer to keep things in the backend code that is specific to a
> given generation.

Agreed, I will post this change soon and will introduce some feature
check as well because we will need it for iommu prot flag as per 
discussion
here - 
https://lore.kernel.org/lkml/20210108181830.GA5457@willie-the-truck/

> > > To solve it in a cleaner way I propose to move it to an a6xx-specific
> > > file, or if it's going to be used with next-gen GPUs, perhaps manage
> > > calling of this code via an adreno quirk/feature in adreno_device.c.
> > > Now that I think about it, A5xx GPMU en/disable could probably managed
> > > like that, instead of using tons of if-statements for each GPU model
> > > that has it..
> > >
> > > While we're at it, do ALL (and I truly do mean ALL, including the
> > > low-end ones, this will be important later on) A6xx GPUs make use of
> > > that feature?
> > >
> >
> > I do not have a list of all A6XX GPUs with me currently, but from what
> > I know, A618, A630, A640, A650 has the support.
>
> From the PoV of bringing up new a6xx, we should probably consider that
> some of them may not *yet* have LLCC enabled.  I have an 8cx laptop
> and once I find time to get the display working, the next step would
> be bringing up a680.. and I'd probably like to start without LLCC..

Right, once I move the LLCC code to a6xx specific address space 
creation,
without LLCC slices for GPU specified in qcom llcc driver, we will not
be using it.

Thanks,
Sai

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