linux-kernel - Re: [PATCH v1] drm/msms/dp: fixed link clock divider bits be over written in BPC unknown case

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Date: Thu, 11 Jan 2024 01:50:37 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc: dri-devel@...ts.freedesktop.org, robdclark@...il.com, sean@...rly.run, 
	swboyd@...omium.org, dianders@...omium.org, vkoul@...nel.org, daniel@...ll.ch, 
	airlied@...il.com, agross@...nel.org, andersson@...nel.org, 
	quic_abhinavk@...cinc.com, quic_jesszhan@...cinc.com, 
	quic_sbillaka@...cinc.com, marijn.suijten@...ainline.org, 
	freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drm/msms/dp: fixed link clock divider bits be over
 written in BPC unknown case

On Wed, 10 Jan 2024 at 22:19, Kuogee Hsieh <quic_khsieh@...cinc.com> wrote:
>
> Since the value of DP_TEST_BIT_DEPTH_8 is already left shifted, in the
> BPC unknown case, the additional shift causes spill over to the other
> bits of the [DP_CONFIGURATION_CTRL] register.
> Fix this by changing the return value of dp_link_get_test_bits_depth()
> in the BPC unknown case to (DP_TEST_BIT_DEPTH_8 >> DP_TEST_BIT_DEPTH_SHIFT).
>
> Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>

For the patch itself:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

Additional note. Since this made me look at how DP_TEST_BIT_DEPTH is
handled in the driver, I stumbled upon dp_link_bit_depth_to_bpc() vs
dp_link_bit_depth_to_bpp(). These two functions look pretty redundant.
Since the former one is used only for the debugfs, please consider
sending a patch that removes it for the sake of using the latter one
and /3 in dp_test_data_show().


-- 
With best wishes
Dmitry