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

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Message-ID: <20210111161115.GB29638@jcrouse1-lnx.qualcomm.com>
Date:   Mon, 11 Jan 2021 09:11:15 -0700
From:   Jordan Crouse <jcrouse@...eaurora.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Rob Clark <robdclark@...il.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Sean Paul <sean@...rly.run>, Jonathan <jonathan@...ek.ca>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Sharat Masetty <smasetty@...eaurora.org>,
        martin.botka@...ainline.org,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Shawn Guo <shawn.guo@...aro.org>,
        marijn.suijten@...ainline.org,
        ~postmarketos/upstreaming@...ts.sr.ht,
        Daniel Vetter <daniel@...ll.ch>,
        angelogioacchino.delregno@...ainline.org,
        Dave Airlie <airlied@...hat.com>, phone-devel@...r.kernel.org,
        freedreno <freedreno@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Freedreno] [PATCH] drm/msm: Only enable A6xx LLCC code on A6xx

On Mon, Jan 11, 2021 at 09:54:12AM +0530, Sai Prakash Ranjan wrote:
> 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@...eaurora.org> 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.

Right. The problem here was that we were assuming an a6xx container in generic
code. Testing the existence of LLCC or not is a different problem but it is my
understanding that if we set the attribute without LLCC enabled it just gets
ignored. Is that correct Sai?

Jordan

> Thanks,
> Sai
> 
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation

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