linux-kernel - Re: [PATCH v2] mtd: mtk-quadspi: add support for DMA reading

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Date:   Mon, 10 Feb 2020 16:30:55 +0800
From:   Yingjoe Chen <yingjoe.chen@...iatek.com>
To:     Chuanhong Guo <gch981213@...il.com>
CC:     <linux-mtd@...ts.infradead.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Richard Weinberger <richard@....at>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] mtd: mtk-quadspi: add support for DMA reading

On Sat, 2020-02-08 at 16:40 +0800, Chuanhong Guo wrote:
> PIO reading mode on this controller is pretty inefficient
> (one cmd+addr+dummy sequence reads only one byte)
> This patch adds support for reading using DMA mode which increases
> reading speed from 1MB/s to 4MB/s
> 
> DMA busy checking is implemented with readl_poll_timeout because
> I don't have access to IRQ-related docs. The speed increment comes
> from those saved cmd+addr+dummy clocks.

Hi Chuanhong,

Thanks for your patch, I'm checking with Guochun to see if we could
release IRQ related information to you.


> This controller requires that DMA source/destination address and
> reading length should be 16-byte aligned. We use a bounce buffer if
> one of them is not aligned, read more than what we need, and copy
> data from corresponding buffer offset.

I've checked with our HW guys. The limitation is on DRAM only.
So for read we should check buffer and length to make sure it is
aligned, but don't need to check from.

Joe.C