linux-kernel - RE: [PATCH] mtd: spi-nor: fsl-quadspi: add big-endian support

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Message-ID: <BLUPR03MB1348A5FF31DA8A5D3302FA483120@BLUPR03MB134.namprd03.prod.outlook.com>
Date:	Thu, 12 Nov 2015 10:07:29 +0000
From:	Yao Yuan <yao.yuan@...escale.com>
To:	Xu Han <han.xu@...escale.com>
CC:	Fabio Estevam <festevam@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Li Leo <LeoLi@...escale.com>,
	Scott Wood <scottwood@...escale.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] mtd: spi-nor: fsl-quadspi: add big-endian support

On Wed, 2015-11-11 at 11:51 -0600, Han Xu wrote:
> On Fri, Oct 30, 2015 at 04:49:41AM -0500, Yuan Yao-B46683 wrote:
> > Hi Fabio Estevam,
> >
> > Thanks for your suggestion.
> > We have an internal discussions for that.
> >
> > We think that:
> > According to the initial commit message of regmap, it is targeting non-
> memory mapped buses. (regmap: Add generic non-memory mapped register
> access API)  But in the imx2_wdt driver, it is used for memory-mapped register
> space.  So it seems that using such a complex framework just to deal with
> endian is an over-kill.
> >
> > when it is not necessary to enable the clock every time we access the register.
> > We don't think it is obvious to us how to use it for handling endianness,
> especially not the way imx2_wdt uses regmap.  __regmap_init_mmio_clk()
> calls regmap_mmio_gen_context() which errors out if reg_format_endian is
> not REGMAP_ENDIAN_DEFAULT or REGMAP_ENDIAN_NATIVE, and elsewhere
> regmap-mmio.c It seems only little-endian accessors.
> >
> > Although it is possible to add the endianness support in the
> > regmap_mmio driver, we don't see too much value in using it especially
> >
> > So we think:
> > static void qspi_writel(struct fsl_qspi *q, u32 val, void __iomem
> > *addr) {
> >       if (q->big_endian)
> >               iowrite32be(val, addr);
> >       else
> >               iowrite32(val, addr);
> > }
> > This way is an easier, more effective solution to do the endian issue.
> >
> > How about your think?
> 
> I think the implement is fine, but I prefer to use quirk rather than read from dts?
> Please also rebase the patch to latest l2-mtd code.
> 

Ok, I will rebase the patch to latest l2-mtd code in the next version.

Thanks.
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