linux-kernel - Re: [PATCH v3 05/15] drm/msm/dpu: fix mixer number counter on allocation

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Message-ID: <da270bd6-3f7a-4100-8352-acbf14b62db5@quicinc.com>
Date: Wed, 8 Jan 2025 17:29:24 -0800
From: Jessica Zhang <quic_jesszhan@...cinc.com>
To: Jun Nie <jun.nie@...aro.org>, Rob Clark <robdclark@...il.com>,
        "Abhinav
 Kumar" <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Simona
 Vetter" <simona@...ll.ch>
CC: <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 05/15] drm/msm/dpu: fix mixer number counter on
 allocation



On 12/18/2024 11:49 PM, Jun Nie wrote:
> Add the case to reserve multiple pairs mixers for high resolution.
> Current code only supports one pair of mixer usage case. To support
> quad-pipe usage case, two pairs of mixers are needed.
> 
> Current code resets number of mixer on failure of pair's peer test and
> retry on another pair. If two pairs are needed, the failure on the test
> of 2nd pair results clearing to the 1st pair. This patch only clear the
> bit for the 2nd pair allocation before retry on another pair.

Hi Jun,

I think the commit message wording is a bit unclear. Maybe something 
like "Reset the current lm_count to an even number instead of completely 
clearing it. This prevents all pairs from being cleared in cases where 
multiple LM pairs are needed"

> 
> Signed-off-by: Jun Nie <jun.nie@...aro.org>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
> index cde3c5616f9bc..a8b01b78c02c7 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
> @@ -316,7 +316,11 @@ static int _dpu_rm_reserve_lms(struct dpu_rm *rm,
>   		if (!rm->mixer_blks[i])
>   			continue;
>   
> -		lm_count = 0;
> +		/*
> +		 * Clear the last bit to drop the previous primary mixer if
> +		 * fail to find its peer.

Same here can we reword it to something like "Reset lm_count to an even 
index. This will drop the previous primary mixer if ..."

> +		 */
> +		lm_count &= 0xfe;

Nit: Can we directly clear the first bit instead of doing an 8-bit bitmask?

Thanks,

Jessica Zhang

>   		lm_idx[lm_count] = i;
>   
>   		if (!_dpu_rm_check_lm_and_get_connected_blks(rm, global_state,
> 
> -- 
> 2.34.1
>