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

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Date: Fri, 05 Jan 2024 10:57:18 +0100
From: Heiko Stübner <heiko@...ech.de>
To: 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>,
 Cristian Ciocaltea <cristian.ciocaltea@...labora.com>,
 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

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>
> > 
> > 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).
> > 
> >> ---
> >>   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.
> 
> 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:

  		/*
		 * if_dclk_rate = dclk_core_rate / K;
  		 * *if_pixclk_div = dclk_rate / if_pixclk_rate;
  		 * *if_dclk_div = dclk_rate / if_dclk_rate;
  		 */

Thanks
Heiko