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

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Date: Fri, 5 Jan 2024 19:49:14 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Heiko Stübner <heiko@...ech.de>,
 Sandy Huang <hjc@...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>,
 Andy Yan <andy.yan@...k-chips.com>
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

On 1/5/24 11:57, Heiko Stübner wrote:
> Hi,
> 
> Am Freitag, 5. Januar 2024, 10:04:55 CET schrieb Andy Yan:
>> On 1/4/24 23:58, Heiko Stübner wrote:
>>> 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>

[...]

>>> 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.
>>
>> This is not a remnant, in my V1, I calculate all the div by formula, but Sascha prefer
>> more for a constants value[0], so I keep this formula as comments to indicate how these value come from.
>>
>> [0]https://patchwork.kernel.org/project/linux-rockchip/patch/20231114112855.1771372-1-andyshrk@163.com/
> 
> thanks for referencing the source of the change.
> Leaving the formula in there was the right choice I think
> 
> That still leaves the issue with the "unused" warning.
> 
> @Christan: in the hdmi block itself can you move the 
> 	if_dclk_rate = dclk_core_rate / K;
> to the comment block please? And possibly reference the use
> of the static values in the comment message.
> 
> The if_dclk_rate var declaration at the top of the function can of course
> go away.
> 
> That way we still keep documenting how these values came to be:

Requested changes submitted via v2:

https://lore.kernel.org/lkml/20240105174007.98054-1-cristian.ciocaltea@collabora.com/

Thanks,
Cristian