linux-kernel - Re: [PATCH 06/19] drm/amd/display/dc/calcs/dce_calcs: Move some large variables from the stack to the heap

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Message-ID: <a74c5599-e519-2b02-f16b-31e352872a31@amd.com>
Date:   Fri, 19 Mar 2021 19:46:54 +0100
From:   Christian König <christian.koenig@....com>
To:     Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexdeucher@...il.com>,
        Lee Jones <lee.jones@...aro.org>
Cc:     Leo Li <sunpeng.li@....com>, LKML <linux-kernel@...r.kernel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        Alex Deucher <alexander.deucher@....com>,
        Colin Ian King <colin.king@...onical.com>,
        Harry Wentland <hwentlan@....com>,
        "Kazlauskas, Nicholas" <nicholas.kazlauskas@....com>
Subject: Re: [PATCH 06/19] drm/amd/display/dc/calcs/dce_calcs: Move some large
 variables from the stack to the heap

Am 19.03.21 um 19:26 schrieb Harry Wentland:
> On 2021-03-19 2:13 p.m., Alex Deucher wrote:
>> + Harry, Nick
>>
>> On Fri, Mar 19, 2021 at 4:24 AM Lee Jones <lee.jones@...aro.org> wrote:
>>>
>>> Fixes the following W=1 kernel build warning(s):
>>>
>>>   drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c: In 
>>> function ‘calculate_bandwidth’:
>>> drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c:2016:1: 
>>> warning: the frame size of 1216 bytes is larger than 1024 bytes 
>>> [-Wframe-larger-than=]
>>>
>>> Cc: Harry Wentland <harry.wentland@....com>
>>> Cc: Leo Li <sunpeng.li@....com>
>>> Cc: Alex Deucher <alexander.deucher@....com>
>>> Cc: "Christian König" <christian.koenig@....com>
>>> Cc: David Airlie <airlied@...ux.ie>
>>> Cc: Daniel Vetter <daniel@...ll.ch>
>>> Cc: Colin Ian King <colin.king@...onical.com>
>>> Cc: amd-gfx@...ts.freedesktop.org
>>> Cc: dri-devel@...ts.freedesktop.org
>>> Signed-off-by: Lee Jones <lee.jones@...aro.org>
>>> ---
>>>   .../gpu/drm/amd/display/dc/calcs/dce_calcs.c  | 32 
>>> ++++++++++++++++---
>>>   1 file changed, 28 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c 
>>> b/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c
>>> index e633f8a51edb6..9d8f2505a61c2 100644
>>> --- a/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c
>>> +++ b/drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c
>>> @@ -98,16 +98,16 @@ static void calculate_bandwidth(
>>>          int32_t num_cursor_lines;
>>>
>>>          int32_t i, j, k;
>>> -       struct bw_fixed yclk[3];
>>> -       struct bw_fixed sclk[8];
>>> +       struct bw_fixed *yclk;
>>> +       struct bw_fixed *sclk;
>>>          bool d0_underlay_enable;
>>>          bool d1_underlay_enable;
>>>          bool fbc_enabled;
>>>          bool lpt_enabled;
>>>          enum bw_defines sclk_message;
>>>          enum bw_defines yclk_message;
>>> -       enum bw_defines tiling_mode[maximum_number_of_surfaces];
>>> -       enum bw_defines surface_type[maximum_number_of_surfaces];
>>> +       enum bw_defines *tiling_mode;
>>> +       enum bw_defines *surface_type;
>>>          enum bw_defines voltage;
>>>          enum bw_defines pipe_check;
>>>          enum bw_defines hsr_check;
>>> @@ -122,6 +122,22 @@ static void calculate_bandwidth(
>>>          int32_t number_of_displays_enabled_with_margin = 0;
>>>          int32_t number_of_aligned_displays_with_no_margin = 0;
>>>
>>> +       yclk = kcalloc(3, sizeof(*yclk), GFP_KERNEL);
>>> +       if (!yclk)
>>> +               return;
>>> +
>>> +       sclk = kcalloc(8, sizeof(*sclk), GFP_KERNEL);
>>> +       if (!sclk)
>>> +               goto free_yclk;
>>> +
>>> +       tiling_mode = kcalloc(maximum_number_of_surfaces, 
>>> sizeof(*tiling_mode), GFP_KERNEL);
>>> +       if (!tiling_mode)
>>> +               goto free_sclk;
>>> +
>>> +       surface_type = kcalloc(maximum_number_of_surfaces, 
>>> sizeof(*surface_type), GFP_KERNEL);
>>> +       if (!surface_type)
>>> +               goto free_tiling_mode;
>>> +
>>
>>
>> Harry or Nick can correct me if I'm wrong, but for this patch and the
>> next one, I think this can be called from an atomic context.
>>
>
> From what I can see this doesn't seem the case. If I'm missing 
> something someone please correct me.

Have you taken into account that using FP functions require atomic 
context as well?

We had quite a bunch of problems with that and had to replace some 
GFP_KERNEL with GFP_ATOMIC in the DC code because of this.

Could of course be that this code here isn't affected by that, but 
better save than sorry.

Christian.

>
> This and the next (06/19) patch are both
> Reviewed-by: Harry Wentland <harry.wentland@....com>
>
> Harry
>
>> Alex
>>
>>>          yclk[low] = vbios->low_yclk;
>>>          yclk[mid] = vbios->mid_yclk;
>>>          yclk[high] = vbios->high_yclk;
>>> @@ -2013,6 +2029,14 @@ static void calculate_bandwidth(
>>>                          }
>>>                  }
>>>          }
>>> +
>>> +       kfree(surface_type);
>>> +free_tiling_mode:
>>> +       kfree(tiling_mode);
>>> +free_yclk:
>>> +       kfree(yclk);
>>> +free_sclk:
>>> +       kfree(sclk);
>>>   }
>>>
>>> /*******************************************************************************
>>> -- 
>>> 2.27.0
>>>
>>> _______________________________________________
>>> dri-devel mailing list
>>> dri-devel@...ts.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel>

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