linux-kernel - Re: [PATCH] spi: mediatek: Manually set dma_ops for spi

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Message-ID: <20170127133621.bifp64y2cdljld65@sirena.org.uk>
Date:   Fri, 27 Jan 2017 13:36:21 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Dmitry Torokhov <dtor@...omium.org>
Cc:     Daniel Kurtz <djkurtz@...omium.org>,
        Robin Murphy <robin.murphy@....com>,
        Leilk Liu <leilk.liu@...iatek.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:SPI SUBSYSTEM" <linux-spi@...r.kernel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Guenter Roeck <groeck@...omium.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] spi: mediatek: Manually set dma_ops for spi_master device

On Thu, Jan 26, 2017 at 09:26:13AM -0800, Dmitry Torokhov wrote:

> OTOH the full buffer used by cros ec *is* DMA-safe (allocated with
> kmalloc), it is that cors ec uses it at offset while transferring data
> piece by piece. Do we want to support this?

I'm not sure the complexity is worth it as a general feature, I worry
about the cost of worrying about cutting the transaction up to include a
PIO portion.  That said that's just a gut feeling, if there were a
sufficiently simple/nice implementation it'd definitely avoid bugs.

To me part of DMA safety is the alignment restrictions.

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