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

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Message-ID: <20200518110150.GX1634618@smile.fi.intel.com>
Date:   Mon, 18 May 2020 14:01:50 +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, 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 Sat, May 16, 2020 at 05:33:53PM +0300, Serge Semin wrote:
> On Fri, May 15, 2020 at 05:01:29PM +0300, Andy Shevchenko wrote:
> > 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.
> 
> It's fixed in a consequent patch anyway. Though if v3 is required I'll remove
> this change from here.

I consider that here you might have introduced a regression and actually doing
two things in one patch. Why not to split?

-- 
With Best Regards,
Andy Shevchenko