[U-Boot] [PATCH] sf: ensure flash device is in 3-byte address mode

[Prabhakar Kushwaha]

Dear Jagan, Simon,

> -----Original Message-----
> From: U-Boot [mailto:u-boot-bounces at lists.denx.de] On Behalf Of Jagan Teki
> Sent: Thursday, December 07, 2017 11:19 AM
> To: Goldschmidt Simon <sgoldschmidt at de.pepperl-fuchs.com>
> Cc: u-boot at lists.denx.de
> Subject: Re: [U-Boot] [PATCH] sf: ensure flash device is in 3-byte address mode
> 
> On Tue, Dec 5, 2017 at 11:50 AM, Goldschmidt Simon
> <sgoldschmidt at de.pepperl-fuchs.com> wrote:
> > + Lukasz (as a reviewer of my patch[1])
> >
> > On Mon, Dec 4, 2017 at 8:20, Jagan Teki wrote:
> >> This is the patch[1] for 4-byte addressing, but I would wonder how can
> proceed
> >> operations with 4-byte if we disable during probe.
> >>
> >> [1]
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgit.denx
> .de%2F%3Fp%3Du-boot-
> &data=02%7C01%7Cprabhakar.kushwaha%40nxp.com%7Ca37e67c0f5fd431396
> 5f08d53d3649b8%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C6364
> 82225771650679&sdata=CBQkKDXTE1g1mvEbYuyiBApW2NTxQFCirGeJV9uzX8E
> %3D&reserved=0
> >> spi.git;a=commitdiff;h=fd0c22a90772379c4c11ba09347d36cc8ee17dca
> >
> > OK, so your patch does something different than what I did.
> >
> > I was trying to keep the change to U-Boot as small as possible, only
> > fixing this issue I was seeing:
> >
> > After a soft-reboot where the SPI chip was not reset, it is left in
> > 4-byte addressing mode (linux uses this mode, obviously). Remember
> > that 4-byte mode is not a permanent setting, so we can enter and
> > leave it any time we like by issuing a command.
> >
> > U-Boot uses the Bank Address Register (BAR) for spi flash chips with
> > more than 16 MByte, so it impclitly assumes that the chip is in
> > 3-byte address mode. As I see it, your patch is worth a discussion
> > named "should we use 4-byte addressing mode on spi flash chips?".
> > I do think this is a better alternative than writing BAR! But this
> > change probably needs discussion and testing.
> 
> OK, will review your patch.
> 

Other solution to this problem could have been "adding support of 4byte addressing". 

There will always be a requirement of supporting >16MB flash.  

--pk