linux-kernel - Re: [PATCH v2 02/19] spi: dw: Add Tx/Rx finish wait methods to the MID DMA

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Message-ID: <20200518111156.GD8699@sirena.org.uk>
Date:   Mon, 18 May 2020 12:11:56 +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>,
        Georgy Vlasov <Georgy.Vlasov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        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>,
        Allison Randal <allison@...utok.net>,
        Gareth Williams <gareth.williams.jx@...esas.com>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "wuxu.wu" <wuxu.wu@...wei.com>, Clement Leger <cleger@...ray.eu>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/19] spi: dw: Add Tx/Rx finish wait methods to the
 MID DMA

On Mon, May 18, 2020 at 02:04:53PM +0300, Serge Semin wrote:
> On Mon, May 18, 2020 at 11:51:30AM +0100, Mark Brown wrote:

> > > - semantically the xfer argument isn't optional and we can't fetch it that easy
> > >   in the dmaengine completion callbacks.

> > Not sure I follow this.

> I mean is it Ok to call the spi_delay_exec like this: spi_delay_exec(delay, NULL),
> with null passed instead of xfer pointer? Semantically the pointer is required only
> if we'd need to calculate the SPI_DELAY_UNIT_SCK delay, but here we'll need
> USECS and NSECS delays. So at the first glace there is no problem with passed
> NULL instead of xfer. But doing so we'd rely on the semantic peculiarity, which
> may seem a bit hackish.

Yes, that should be fine if you don't specify a SCK delay.  There's no
reason to be looking at that if the delay isn't specified in SCKs.

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