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 for linux-mtd@lists.infradead.org; Mon, 03 Dec 2018 09:08:38 +0000
Date: Mon, 3 Dec 2018 10:08:14 +0100
From: Boris Brezillon <boris.brezillon@bootlin.com>
To: "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@nokia.com>
Cc: "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>, Marek
 Vasut <marek.vasut@gmail.com>, David Woodhouse <dwmw2@infradead.org>, Brian
 Norris <computersforpeace@gmail.com>, Richard Weinberger <richard@nod.at>,
 Tudor Ambarus <tudor.ambarus@microchip.com>
Subject: Re: [PATCH] mtd: spi-nor: Provide default address width and latency
 for map selection
Message-ID: <20181203100814.095a12f4@bbrezillon>
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On Mon, 3 Dec 2018 08:37:17 +0000
"Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@nokia.com>
wrote:

> Hi!
> 
> On 03/12/2018 09:23, Boris Brezillon wrote:
> >> This is the same instruction 65h which is used to read regs and which
> >> appears in SMPT headers, it is a chicken-egg problem.  
> > Oh, right, I remember now. Not a smart decision from Spansion :-/.
> >   
> >> Therefore, I don't know if it's possible to provide smarter heuristics
> >> here.  
> > Maybe:
> > 
> > ref_cr1 = read_CR1_using_RDCR()
> > 
> > for_each_possible_dummy_and_addr_width
> > 	cr1 = read_CR1_using_RDAR()
> > 	if (cr1 == ref_cr1)
> > 		break;  
> 
> This will not work, as default value for CR1(N)V is 0 and that is the value
> one gets with incorrect addr_width as well.
> 

How about:

	// set the WE bit in SR1 so that SR1 is not 0
	write_enable()

	ref_sr1 = read_SR1_using_RDSR1()
	for_each_possible_dummy_and_addr_width
	sr1 = read_SR1_using_RDAR()
	if (sr1 == ref_sr1)
		break;

	write_disable()