linux-kernel - Re: [PATCH 11/15] drm/mediatek: Support CRC in VDOSYS0

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Message-ID: <476caaedd26b90ac4af51d783026e99468be5721.camel@mediatek.com>
Date:   Wed, 30 Aug 2023 05:13:39 +0000
From:   Shawn Sung (宋孝謙) 
        <Shawn.Sung@...iatek.com>
To:     "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        CK Hu (胡俊光) <ck.hu@...iatek.com>,
        "airlied@...il.com" <airlied@...il.com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>,
        Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH 11/15] drm/mediatek: Support CRC in VDOSYS0

Hi CK,

On Thu, 2023-08-24 at 02:29 +0000, CK Hu (胡俊光) wrote:
> 
> Read CRC by CPU in ovl irq handler instead of using cmdq, so things
> would be simpler.
> 

CPU is less reliable than GCE in terms of CRC retrieval because:
1. Slower read/write register speed (1/15 of GCE)
2. The time ISR being executed is not controllable
3. CPU and bus could be busy, or the clock rate is low at the time

Although we do have a CPU version, there is about a 5% chance to
fail if the CPU clock rate is not set to the maximum,
therefore, we choose GCE (CMDQ) to do the job for better stability.

Will mention this in the cover letter in the next version.

Thanks,

Hsiao Chien Sung