linux-kernel - Re: [V5 PATCH 1/1] driver:mtd:spi-nor: Add quad I/O support for Micron spi nor

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Message-ID: <20141127091448.GU3212@norris-Latitude-E6410>
Date:	Thu, 27 Nov 2014 01:14:48 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	bpqw <bpqw@...ron.com>
Cc:	Marek Vasut <marex@...x.de>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"shijie8@...il.com" <shijie8@...il.com>,
	"geert+renesas@...der.be" <geert+renesas@...der.be>,
	"grmoore@...era.com" <grmoore@...era.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [V5 PATCH 1/1] driver:mtd:spi-nor: Add quad I/O support for
 Micron spi nor

On Thu, Nov 27, 2014 at 05:55:43AM +0000, bpqw wrote:

> >What's the difference between using EVCR and the ENTER QUAD I/O MODE
> >(35h) command I see in some of your datasheets? Are both supported on all Micron quad I/O SPI NOR flash?
> 
> There is no difference between using EVCR and the ENTER QUAD I/O MODE command.
> But, for some Micron spi nor, there no ENTER Quad I/O command(35h),such as n25q064.
> for all current Micron spi nor, if it support quad I/O mode, Using EVCR definitely be supported.
> So, we recommend that enable QUAD I/O mode by writing ECVR.

Good to know. Thanks for the info. Maybe you can note this somewhere in
your next version, like a comment in the commit description.

> >Also, which SPI NOR is this enabled for? I don't see any Micron entries in spi_nor_ids[] which contain the SPI_NOR_QUAD_READ flag.
> 
> Yes, we now don't see any Micron entries in spi_nor_ids[] which
> contain the SPI_NOR_QUAD_READ flag. But Micron spi nor in
> spi_nor_ids[] all support Quad I/O mode.

Then add them! At least, for flash that support them (for all packages
that might share the same ID).

> maybe customer want to use default mode(extended I/O mode),
> When submitted relevant patch, they didn't SPI_NOR_QUAD_READ flag in the spi_nor_ids[].

The flag may have been omitted because it didn't exist at the time. Or
it didn't get tested.

Regardless, just because you enable this flag in spi_nor_ids[] doesn't
mean that it will enable Quad I/O for users that can't support it; board
files / DT descriptions still have to opt in by advertising hardware
support for Quad I/O.

See, for example, spi-tx-bus-width and spi-rx-bus-width properties in
Documentation/devicetree/bindings/spi/spi-bus.txt.

> This patch is just for wanting to enable Micron Quad I/O mode.

That's fine. But I'd welcome any follow-up patch to add the QUAD flag to
the right Micron table entries. Otherwise, this patch doesn't actually
help anyone.

BTW, given that you aren't changing any entries to spi_nor_ids[] yet,
have you actually tested this patch? Or are you only working off the
specifications / datasheets?

Thanks,
Brian
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