linux-kernel - Re: [PATCH v2 4/6] dmaengine: dw: Print warning if multi-block is unsupported

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Date:   Mon, 11 May 2020 22:32:23 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Vinod Koul <vkoul@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] dmaengine: dw: Print warning if multi-block is
 unsupported

On Mon, May 11, 2020 at 09:32:47PM +0300, Serge Semin wrote:

> Thanks for the explanation. Max segment size being set to the DMA controller generic
> device should work well. There is no need in setting the transfer and messages
> size limitations. Besides I don't really see the
> max_transfer_size/max_message_size callbacks utilized in the SPI core. These
> functions are called in the spi-mem.c driver only. Do I miss something?

We really should validate them in the core but really they're intended
for client drivers (like spi-mem kind of is) to allow them to adapt the
sizes of requests they're generating so the core never sees anything
that's too big.  For the transfers we have a spi_split_transfers_maxsize()
helper if anything wants to use it.  Fortunately there's not that many
controllers with low enough limits to worry about so actual usage hasn't
been that high.

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