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Date:   Tue, 11 Apr 2023 18:50:24 -0700
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Subject: Re: [Freedreno] [PATCH] drm/msm/dpu: add DSC range checking during
 resource reservation
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To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Marijn Suijten <marijn.suijten@somainline.org>,
        Kuogee Hsieh <quic_khsieh@quicinc.com>
CC:     <freedreno@lists.freedesktop.org>, <quic_sbillaka@quicinc.com>,
        <airlied@gmail.com>, <andersson@kernel.org>, <robdclark@gmail.com>,
        <dri-devel@lists.freedesktop.org>, <dianders@chromium.org>,
        <vkoul@kernel.org>, <agross@kernel.org>, <daniel@ffwll.ch>,
        <linux-arm-msm@vger.kernel.org>, <swboyd@chromium.org>,
        <sean@poorly.run>, <linux-kernel@vger.kernel.org>
References: <1681247380-1607-1-git-send-email-quic_khsieh@quicinc.com>
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 <24c5aa23-9b3c-787c-10aa-e9d5ad91512b@linaro.org>
From:   Abhinav Kumar <quic_abhinavk@quicinc.com>
In-Reply-To: <24c5aa23-9b3c-787c-10aa-e9d5ad91512b@linaro.org>
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On 4/11/2023 6:06 PM, Dmitry Baryshkov wrote:
> On 12/04/2023 01:32, Abhinav Kumar wrote:
>> Hi Marijn
>>
>> On 4/11/2023 3:24 PM, Marijn Suijten wrote:
>>> Again, don't forget to include previous reviewers in cc, please :)
>>>
>>> On 2023-04-11 14:09:40, Kuogee Hsieh wrote:
>>>> Perform DSC range checking to make sure correct DSC is requested before
>>>> reserve resource for it.
> 
> nit: reserving
> 
>>>
>>> This isn't performing any range checking for resource reservations /
>>> requests: this is only validating the constants written in our catalog
>>> and seems rather useless.  It isn't fixing any real bug either, so the
>>> Fixes: tag below seems extraneous.
>>>
>>> Given prior comments from Abhinav that "the kernel should be trusted",
>>> we should remove this validation for all the other blocks instead.
>>>
>>
>> The purpose of this check is that today all our blocks in RM use the 
>> DSC_* enum as the size.
>>
>> struct dpu_hw_blk *dsc_blks[DSC_MAX - DSC_0];
>>
>> If the device tree ends up with more DSC blocks than the DSC_* enum, 
>> how can we avoid this issue today? Not because its a bug in device 
>> tree but how many static number of DSCs are hard-coded in RM.
> 
> We don't have these blocks in device tree. And dpu_hw_catalog shouldn't 
> use indices outside of enum dpu_dsc.
> 

ah, my bad, i should have said catalog here. Okay so the expectation is 
that dpu_hw_catalog.c will program the indices to match the RM limits.

I still stand by the fact that the hardware capabilities coming from 
catalog should be trusted but this is just the SW index.

> Marijn proposed to pass struct dpu_foo_cfg directly to 
> dpu_hw_foo_init(). This will allow us to drop these checks completely.
> 

Ah okay, sure, would like to see that then uniformly get rid of these 
checks.

> For the time being, I think it might be better to add these checks for 
> DSC for the sake of uniformity.
> 

Yes, i think so too.

>>
>> And like you said, this is not specific to DSC. Such checks are 
>> present for other blocks too.
>>
>>>> Fixes: c985d7bb64ff ("drm/msm/disp/dpu1: Add DSC support in RM")
>>>> Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
>>>> ---
>>>>   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 10 +++++++++-
>>>>   1 file changed, 9 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c 
>>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
>>>> index f4dda88..95e58f1 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
>>>> @@ -1,6 +1,7 @@
>>>>   // SPDX-License-Identifier: GPL-2.0-only
>>>>   /*
>>>>    * Copyright (c) 2016-2018, The Linux Foundation. All rights 
>>>> reserved.
>>>> + * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights 
>>>> reserved.
>>>>    */
>>>>   #define pr_fmt(fmt)    "[drm:%s] " fmt, __func__
>>>> @@ -250,6 +251,11 @@ int dpu_rm_init(struct dpu_rm *rm,
>>>>           struct dpu_hw_dsc *hw;
>>>>           const struct dpu_dsc_cfg *dsc = &cat->dsc[i];
>>>> +        if (dsc->id < DSC_0 || dsc->id >= DSC_MAX) {
>>>> +            DPU_ERROR("skip dsc %d with invalid id\n", dsc->id);
>>>> +            continue;
>>>> +        }
>>>> +
>>>>           hw = dpu_hw_dsc_init(dsc->id, mmio, cat);
>>>>           if (IS_ERR_OR_NULL(hw)) {
>>>>               rc = PTR_ERR(hw);
>>>> @@ -557,8 +563,10 @@ static int _dpu_rm_make_reservation(
>>>>       }
>>>>       ret  = _dpu_rm_reserve_dsc(rm, global_state, enc, 
>>>> &reqs->topology);
>>>> -    if (ret)
>>>> +    if (ret) {
>>>> +        DPU_ERROR("unable to find appropriate DSC\n");
>>>
>>> This, while a nice addition, should go in a different patch.
> 
> I'd agree here, a separate patch.
> 
>>>
>>> Thanks!
>>>
>>> - Marijn
>>>
>>>>           return ret;
>>>> +    }
>>>>       return ret;
>>>>   }
>>>> -- 
>>>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>>>> Forum,
>>>> a Linux Foundation Collaborative Project
>>>>
>