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Date:   Wed, 6 May 2020 15:10:28 +0530
From:   Pratyush Yadav <me@yadavpratyush.com>
To:     masonccyang@mxic.com.tw
Cc:     Boris Brezillon <boris.brezillon@collabora.com>,
        broonie@kernel.org, juliensu@mxic.com.tw,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
        linux-spi@vger.kernel.org, miquel.raynal@bootlin.com,
        Pratyush Yadav <p.yadav@ti.com>, richard@nod.at,
        tudor.ambarus@microchip.com, vigneshr@ti.com
Subject: Re: [PATCH v2 0/5] mtd: spi-nor: Add support for Octal 8D-8D-8D mode
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On 05/05/20 05:31PM, masonccyang@mxic.com.tw wrote:
> Hi Pratyush,
> > > I can't apply your patches to enable xSPI Octal mode for 
> > > mx25uw51245g because your patches set up Octal protocol first and 
> > > then using Octal protocol to write Configuration Register 2(CFG 
> > > Reg2). I think driver
> > > should write CFG Reg2 in SPI 1-1-1 mode (power on state) and make sure
> > > write CFG Reg 2 is success and then setup Octa protocol in the last.
> > 
> > Register writes should work in 1S mode, because nor->reg_proto is only 
> > set _after_ 8D mode is enabled (see spi_nor_octal_dtr_enable()). In 
> > fact, both patch 15 and 16 in my series use register writes in 1S mode.
> 
> but I didn't see driver roll back "nor->read/write_proto = 1" 
> if xxx->octal_dtr_enable() return failed!

I copied what spi_nor_quad_enable() did, and made failure fatal. So if 
xxx->octal_dtr_enable() fails, the probe would fail and the flash would 
be unusable. You can try your hand at a fallback system where you try 
all possible protocols available, but I think that should be a different 
patchset.

-- 
Regards,
Pratyush Yadav