linux-kernel - Re: [PATCH 2/3] spi: Add HiSilicon v3xx SPI NOR flash controller driver

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Message-ID: <20191105110504.GA4500@sirena.co.uk>
Date:   Tue, 5 Nov 2019 11:05:05 +0000
From:   Mark Brown <broonie@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     marek.vasut@...il.com, tudor.ambarus@...rochip.com,
        linuxarm@...wei.com, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-spi@...r.kernel.org,
        xuejiancheng@...ilicon.com, fengsheng5@...wei.com
Subject: Re: [PATCH 2/3] spi: Add HiSilicon v3xx SPI NOR flash controller
 driver

On Tue, Nov 05, 2019 at 10:58:39AM +0000, John Garry wrote:
> On 04/11/2019 19:24, Mark Brown wrote:
> > On Tue, Nov 05, 2019 at 12:51:36AM +0800, John Garry wrote:

> > > +		if (len) {
> > > +			u32 val;
> > > +
> > > +			val = __raw_readl(host->regbase + CMD_DATABUF(words));
> > > +
> > > +			to += words * 4;
> > > +			for (i = 0; i < len; i++, val >>= 8, to++)
> > > +				*to = (u8)val;
> > > +		}
> > > +	} else {
> > > +		for (i = 0; i < DIV_ROUND_UP(len, 4); i++) {
> > > +			u32 val = __raw_readl(host->regbase + CMD_DATABUF(i));
> > > +			int j;

> > The more usual pattern for these would be to do some unaligned accesses
> > for the start/end of the buffer to get to alignment and then transfer
> > the rest as aligned data.

> Yeah, I understand you, but for that I would need to generate multiple
> transactions in the driver, and I wanted to keep 1x transaction per
> spi_controller_mem_ops.exec_op call.

> So maybe I can do some trickery in my adjust_op_size method to generate
> these multiple transactions: a. any unaligned start data b. the 32b-aligned
> data b. unaligned end. I think that the HW should be able to handle that.

Right, that's what I was expecting.

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