Re: [PATCH] Check flag status register for Micron n25q512a

[Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>]

On Thursday, February 27, 2014 at 08:33:14 AM, Brian Norris wrote:
> + Marek

Thanks, I really need to subscribe to this ML ;-/

> Hi Insop,
> 
> On Mon, Jan 06, 2014 at 05:21:17AM +0000, Insop Song wrote:
> > In order to use Micron n25q512a, MTD, two changes are required as
> > follows: - jedec code should be fixed
> 
> I have a feeling there are more than one "n25q512a" device, with
> different IDs.

ACK, I have similar feeling. Jain, can you tell us the precise marking on your 
N25Q512A chip (that is, every single letter on the top of the chip package 
exactly as it is engraved there ) please? Or make a photo ...

Insop, can you please do the same ?

[...]

> > @@ -782,7 +864,7 @@ static const struct spi_device_id m25p_ids[] = {
> > 
> >  	{ "n25q128a11",  INFO(0x20bb18, 0, 64 * 1024,  256, 0) },
> >  	{ "n25q128a13",  INFO(0x20ba18, 0, 64 * 1024,  256, 0) },
> >  	{ "n25q256a",    INFO(0x20ba19, 0, 64 * 1024,  512, SECT_4K) },
> > 
> > -	{ "n25q512a",    INFO(0x20bb20, 0, 64 * 1024, 1024, SECT_4K) },
> > +	{ "n25q512a",    INFO(0x20ba20, 0, 64 * 1024, 1024, SECT_4K) },
> 
> You probably want to figure out the distinction between the old table
> entry and the new one, and assign your new entry a new string
> accordingly.

ACK. The datasheet actually claims this change is correct, see [1] (page 40, 
table 21), but as we know, Micron really does shitty job when it comes to using 
the JEDEC IDs for it's chips.

> >  	/* PMC */
> >  	{ "pm25lv512",   INFO(0,        0, 32 * 1024,    2, SECT_4K_PMC) },
> > 
> > @@ -996,6 +1078,13 @@ static int m25p_probe(struct spi_device *spi)
> > 
> >  	spi_set_drvdata(spi, flash);
> >  	
> >  	/*
> > 
> > +	 * Micron n25q512a requires to check flag status register
> > +	 */
> > +	flash->flag_status = false;
> > +	if (strcmp(id->name, "n25q512a") == 0)
> > +		flash->flag_status = true;;
> 
> This doesn't look good at all. If any other flash start to need this, we
> don't want to code each ID string here. That's fragile and
> non-scaleable. If we need this option, you need to add another flag to
> the m25p_ids[] table, I guess...

This waiting for some bit in FSR looks like it can be wrapped into 
wait_till_ready(), no ?

What I cannot find in the datasheet though is any evidence which would clearly 
mandate the use of FSR bit 0x80 to test if the chip is ready for next operation 
instead of using the regular STATUS register bit . Insop, can you please 
elaborate on why using the FSR is needed ?

[1] 
https://www.micron.com/~/media/Documents/Products/Data%20Sheet/NOR%20Flash/Serial%20NOR/N25Q/n25q_512mb_1ce_3v_65nm.pdf
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