linux-kernel - Re: [PATCH] drm/rockchip: vop2: Drop unused if_dclk

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Message-ID: <b017a3e2-f658-4a95-b972-6ffb87acfdc3@collabora.com>
Date: Thu, 4 Jan 2024 21:12:25 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Heiko Stübner <heiko@...ech.de>,
 Sandy Huang <hjc@...k-chips.com>, Andy Yan <andy.yan@...k-chips.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
 kernel@...labora.com
Subject: Re: [PATCH] drm/rockchip: vop2: Drop unused if_dclk_rate variable

Hi Heiko,

On 1/4/24 17:58, Heiko Stübner wrote:
> Hi Christian, Andy,
> 
> Am Donnerstag, 4. Januar 2024, 15:39:50 CET schrieb Cristian Ciocaltea:
>> Commit 5a028e8f062f ("drm/rockchip: vop2: Add support for rk3588")
>> introduced a variable which ended up being unused.  Remove it.
>>
>> rockchip_drm_vop2.c:1688:23: warning: variable ‘if_dclk_rate’ set but not used [-Wunused-but-set-variable]
>>
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
> 
> in general, please don't send non-series patches as replies to other patches.
> It confuses tooling like b4 way too often, as this patch is not designated
> as a 2/2 (similar to the first one not being 1/2).

That was unintentional, sorry!  I wrongly assumed 'git send-email' is
able to correctly handle multiple patches which are not part of a
series.  I'm not sure if the '--no-thread' flag would have helped.

>> ---
>>  drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
>> index 44508c2dd614..923985d4161b 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
>> @@ -1685,7 +1685,6 @@ static unsigned long rk3588_calc_cru_cfg(struct vop2_video_port *vp, int id,
>>  	unsigned long dclk_core_rate = v_pixclk >> 2;
>>  	unsigned long dclk_rate = v_pixclk;
>>  	unsigned long dclk_out_rate;
>> -	unsigned long if_dclk_rate;
>>  	unsigned long if_pixclk_rate;
>>  	int K = 1;
>>  
>> @@ -1700,7 +1699,6 @@ static unsigned long rk3588_calc_cru_cfg(struct vop2_video_port *vp, int id,
>>  		}
>>  
>>  		if_pixclk_rate = (dclk_core_rate << 1) / K;
>> -		if_dclk_rate = dclk_core_rate / K;
>>  		/*
>>  		 * *if_pixclk_div = dclk_rate / if_pixclk_rate;
>>  		 * *if_dclk_div = dclk_rate / if_dclk_rate;
>>  		 */
> 		*if_pixclk_div = 2;
> 		*if_dclk_div = 4;
> 
> with the code continuing with those static constants but the comment
> showing a forumula, I do hope Andy can provide a bit of insight into
> what is happening here.
> 
> I.e. I'd really like to understand if that really is just a remnant or
> something different is needed.

The current implementation is not able to handle all display modes
supported by connected displays, e.g. in my testing environment I
encountered issues with 2560x1440-75.00Hz, 2048x1152-60.00Hz,
1024x768-60.00Hz.  Additionally, it doesn't seem to cope well with
non-integer refresh rates like 59.94, 29.97, 23.98, etc.

My temporary workaround relies on using the HDMI PHY PLL in conjunction
with a downstream-based hack to compute the clock rates.  I'm not sure
that would be an upstreamable solution, so I would let Andy shed some
light on the topic.

Thanks,
Cristian

> 
> Heiko
> 
>