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 for linux-mtd@lists.infradead.org; Mon, 03 Dec 2018 09:35:14 +0000
Date: Mon, 3 Dec 2018 10:34:50 +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: <20181203103450.61a8d98f@bbrezillon>
In-Reply-To: <20181203100814.095a12f4@bbrezillon>
References: <20181129181519.15681-1-alexander.sverdlin@nokia.com>
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On Mon, 3 Dec 2018 10:08:14 +0100
Boris Brezillon <boris.brezillon@bootlin.com> wrote:

> 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;

Oh, and you should read CR2 to make sure AL and RL fields match the
selected addr/dummy values.

> 
> 	write_disable()