Re: [PATCH] mtd: spi-nor: Provide default address width and latency for map selection

[Boris Brezillon <boris.brezillon@bootlin.com>]

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()