linux-kernel - Re: [PATCH v2 09/19] spi: dw: Parameterize the DMA Rx/Tx burst length

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Message-ID: <20200515140129.GD1634618@smile.fi.intel.com>
Date:   Fri, 15 May 2020 17:01:29 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Mark Brown <broonie@...nel.org>,
        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>,
        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>,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@...el.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/19] spi: dw: Parameterize the DMA Rx/Tx burst length

On Fri, May 15, 2020 at 01:47:48PM +0300, Serge Semin wrote:
> It isn't good to have numeric literals in the code especially if there
> are multiple of them and they are related. Moreover in current
> implementation the Tx DMA transfer activation level isn't optimal,
> since it's hardwired to be at 16-32 bytes level, while it's better
> to keep the SPI FIFO buffer as full as possible until all available
> data is submitted. So lets introduce the DMA burst level
> parametrization macros with optimal values - issue Rx transfer if at
> least 16 bytes are available in the buffer and execute Tx transaction
> if at least 16 bytes room is opened in SPI Tx FIFO.

> -	dw_writel(dws, DW_SPI_DMARDLR, 0xf);
> -	dw_writel(dws, DW_SPI_DMATDLR, 0x10);
> +	dw_writel(dws, DW_SPI_DMARDLR, RX_BURST_LEVEL - 1);
> +	dw_writel(dws, DW_SPI_DMATDLR, dws->fifo_len - TX_BURST_LEVEL);

...and if FIFO length is less than TX_BURST_LEVEL?

For the patch that introduces definitions, i.e. keeping the last line here as

	dw_writel(dws, DW_SPI_DMATDLR, TX_BURST_LEVEL);

I'm good. You may put your tag in that case. For fifo_len case we need to
discuss in separate patch, perhaps.

-- 
With Best Regards,
Andy Shevchenko