linux-kernel - Re: [PATCH 07/17] spi: dw: Add Tx/Rx finish wait methods to DMA

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Message-ID: <20200513113656.GF4803@sirena.org.uk>
Date:   Wed, 13 May 2020 12:36:56 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Serge Semin <fancer.lancer@...il.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>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Gareth Williams <gareth.williams.jx@...esas.com>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "wuxu.wu" <wuxu.wu@...wei.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/17] spi: dw: Add Tx/Rx finish wait methods to DMA

On Wed, May 13, 2020 at 02:35:55PM +0300, Serge Semin wrote:
> On Fri, May 08, 2020 at 06:30:23PM +0100, Mark Brown wrote:

> > > +	while (dw_spi_dma_tx_busy(dws) && retry--)
> > > +		ndelay(ns);

> > How deep can the FIFO be with this IP - could we end up ndelay()ing for
> > non-trivial amounts of time?

> According to the DW APB SSI db it can be up to 256 transfer words. So the delay
> should be trivial.

Yes, that should be fine.

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