From: David Laight <David.Laight@ACULAB.COM>
To: 'Bert Vermeulen' <bert@biot.com>, Pratyush Yadav <p.yadav@ti.com>
Cc: "vigneshr@ti.com" <vigneshr@ti.com>,
"tudor.ambarus@microchip.com" <tudor.ambarus@microchip.com>,
"richard@nod.at" <richard@nod.at>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
"miquel.raynal@bootlin.com" <miquel.raynal@bootlin.com>
Subject: RE: [PATCH] mtd: spi-nor: Fix 3-or-4 address byte mode logic
Date: Fri, 2 Oct 2020 07:50:38 +0000 [thread overview]
Message-ID: <1c4ee46115854ce28b17935504f2fc78@AcuMS.aculab.com> (raw)
In-Reply-To: <801445c9-4f59-5300-3a03-b48a3d631efe@biot.com>
From: Bert Vermeulen
> Sent: 01 October 2020 23:23
>
> On 10/1/20 8:34 AM, Pratyush Yadav wrote:
> > So using an address width of 4 here is not necessarily the right thing
> > to do. This change would break SMPT parsing for all flashes that use
> > 3-byte addressing by default because SMPT parsing can involve register
> > reads/writes. One such device is the Cypress S28HS flash. In fact, this
> > was what prompted me to write the patch [0].
> >
> > Before that patch, how did MX25L25635F decide to use 4-byte addressing?
>
> The SoCs I'm dealing with have an SPI_ADDR_SEL pin, indicating whether it
> should be in 3 or 4-byte mode. The vendor's hacked-up U-Boot sets the mode
> accordingly, as does their BSP. It seems to me like a misfeature, and I want
> to just ignore it and do reasonable JEDEC things, but I have the problem
> that the flash chip can be in 4-byte mode by the time it gets to my spi-nor
> driver.
If these are the devices I think they are, can't you read the
non-volatile config word (bit 0) to find out whether the device
expects a 3 or 4 byte address and how many 'idle' clocks there
are before the read data?
A device that requires 3 bytes of address can be set to a read
delay of 12 cycles (rather than the usual 10) so that 'hardware'
reads (typically from address 0) can transparently support
devices that require 3 or 4 bytes addresses.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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next prev parent reply other threads:[~2020-10-02 7:51 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-30 23:56 [PATCH] mtd: spi-nor: Fix 3-or-4 address byte mode logic Bert Vermeulen
2020-10-01 6:34 ` Pratyush Yadav
2020-10-01 14:15 ` Tudor.Ambarus
2020-10-01 22:22 ` Bert Vermeulen
2020-10-02 7:50 ` David Laight [this message]
2020-10-04 21:12 ` Bert Vermeulen
2020-10-04 21:36 ` David Laight
2020-10-06 23:19 ` Joel Stanley
2020-10-06 11:03 ` Tudor.Ambarus
2020-10-06 11:19 ` Tudor.Ambarus
2020-10-06 11:40 ` Pratyush Yadav
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