linux-kernel - Re: [Freedreno] [PATCH] drm/msm/dpu: add DSC range checking during resource reservation

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Message-ID: <24c5aa23-9b3c-787c-10aa-e9d5ad91512b@linaro.org>
Date:   Wed, 12 Apr 2023 04:06:48 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     freedreno@...ts.freedesktop.org, quic_sbillaka@...cinc.com,
        airlied@...il.com, andersson@...nel.org, robdclark@...il.com,
        dri-devel@...ts.freedesktop.org, dianders@...omium.org,
        vkoul@...nel.org, agross@...nel.org, daniel@...ll.ch,
        linux-arm-msm@...r.kernel.org, swboyd@...omium.org,
        sean@...rly.run, linux-kernel@...r.kernel.org
Subject: Re: [Freedreno] [PATCH] drm/msm/dpu: add DSC range checking during
 resource reservation

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.

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

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

> 
> 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@...cinc.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
>>>

-- 
With best wishes
Dmitry