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

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Date:   Mon, 18 May 2020 13:55:34 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Mark Brown <broonie@...nel.org>,
        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 Fri, May 15, 2020 at 10:40:58PM +0300, Serge Semin wrote:
> On Fri, May 15, 2020 at 03:01:11PM +0300, Andy Shevchenko wrote:
> > On Fri, May 15, 2020 at 01:47:41PM +0300, Serge Semin wrote:
> > > Since DMA transfers are performed asynchronously with actual SPI
> > > transaction, then even if DMA transfers are finished it doesn't mean
> > > all data is actually pushed to the SPI bus. Some data might still be
> > > in the controller FIFO. This is specifically true for Tx-only
> > > transfers. In this case if the next SPI transfer is recharged while
> > > a tail of the previous one is still in FIFO, we'll loose that tail
> > > data. In order to fix this lets add the wait procedure of the Tx/Rx
> > > SPI transfers completion after the corresponding DMA transactions
> > > are finished.

...

> > You forgot a Fixes tag.
> 
> If you find a commit this patch fixes I'd be glad to add the tag.)

I believe you can do it, but I will help you here, what about

7063c0d942a1 ("spi/dw_spi: add DMA support")

or may be more closer to the reality

30c8eb52cc4a ("spi: dw-mid: split rx and tx callbacks when DMA")

?

...

> I will if v3 is needed.

I guess it will be due to Fixes tag.

-- 
With Best Regards,
Andy Shevchenko