[PATCH RESEND] drm/amd/display: Fix division by zero in setup_dsc_config

[Rodrigo Siqueira Jordao]

On 4/22/24 8:35 AM, Jose Fernandez wrote:
> When slice_height is 0, the division by slice_height in the calculation
> of the number of slices will cause a division by zero driver crash. This
> leaves the kernel in a state that requires a reboot. This patch adds a
> check to avoid the division by zero.
> 
> The stack trace below is for the 6.8.4 Kernel. I reproduced the issue on
> a Z16 Gen 2 Lenovo Thinkpad with a Apple Studio Display monitor
> connected via Thunderbolt. The amdgpu driver crashed with this exception
> when I rebooted the system with the monitor connected.
> 
> kernel: ? die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434 arch/x86/kernel/dumpstack.c:447)
> kernel: ? do_trap (arch/x86/kernel/traps.c:113 arch/x86/kernel/traps.c:154)
> kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
> kernel: ? do_error_trap (./arch/x86/include/asm/traps.h:58 arch/x86/kernel/traps.c:175)
> kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
> kernel: ? exc_divide_error (arch/x86/kernel/traps.c:194 (discriminator 2))
> kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
> kernel: ? asm_exc_divide_error (./arch/x86/include/asm/idtentry.h:548)
> kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
> kernel: dc_dsc_compute_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1109) amdgpu
> 
> After applying this patch, the driver no longer crashes when the monitor
> is connected and the system is rebooted. I believe this is the same
> issue reported for 3113.
> 
> Signed-off-by: Jose Fernandez <josef at netflix.com>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3113
> ---
>   drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
> index ac41f9c0a283..597d5425d6cb 100644
> --- a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
> +++ b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
> @@ -1055,7 +1055,12 @@ static bool setup_dsc_config(
>   	if (!is_dsc_possible)
>   		goto done;
>   
> -	dsc_cfg->num_slices_v = pic_height/slice_height;
> +	if (slice_height > 0)
> +		dsc_cfg->num_slices_v = pic_height/slice_height;

Hi Jose,

First of all, thanks a lot for your patch.

Your patch looks good; I just added {} in the if and spaces around '/' 
before merging your patch.

Anyway,

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>

Thanks
Siqueira

> +	else {
> +		is_dsc_possible = false;
> +		goto done;
> +	}
>   
>   	if (target_bandwidth_kbps > 0) {
>   		is_dsc_possible = decide_dsc_target_bpp_x16(