Re: [PATCH v2 0/5] mtd: spi-nor: Add support for Octal 8D-8D-8D mode

From: Vignesh Raghavendra <vigneshr@ti.com>
To: Boris Brezillon <boris.brezillon@collabora.com>,
	Mason Yang <masonccyang@mxic.com.tw>
Cc: <broonie@kernel.org>, <tudor.ambarus@microchip.com>,
	<miquel.raynal@bootlin.com>, <richard@nod.at>,
	<juliensu@mxic.com.tw>, <linux-kernel@vger.kernel.org>,
	<linux-mtd@lists.infradead.org>, <linux-spi@vger.kernel.org>,
	Pratyush Yadav <p.yadav@ti.com>
Subject: Re: [PATCH v2 0/5] mtd: spi-nor: Add support for Octal 8D-8D-8D mode
Date: Tue, 21 Apr 2020 15:05:08 +0530	[thread overview]
Message-ID: <56365995-fe30-534f-9dbc-7307d9b9f846@ti.com> (raw)
In-Reply-To: <20200421092328.129308f6@collabora.com>

On 21/04/20 12:53 pm, Boris Brezillon wrote:
> +Pratyush who's working on a similar patchet [1].
> 
> Hello Mason,
> 
> On Tue, 21 Apr 2020 14:39:42 +0800
> Mason Yang <masonccyang@mxic.com.tw> wrote:
> 
>> Hello,
>>
>> This is repost of patchset from Boris Brezillon's
>> [RFC,00/18] mtd: spi-nor: Proposal for 8-8-8 mode support [1].
> 
> I only quickly went through the patches you sent and saying it's a
> repost of the RFC is a bit of a lie. You completely ignored the state
> tracking I was trying to do to avoid leaving the flash in 8D mode when
> suspending/resetting the board, and I think that part is crucial. If I
> remember correctly, we already had this discussion so I must say I'm a
> bit disappointed.
> 
> Can you sync with Pratyush? I think his series [1] is better in that it
> tries to restore the flash in single-SPI mode before suspend (it's
> missing the shutdown case, but that can be easily added I think). Of
> course that'd be even better to have proper state tracking at the SPI
> NOR level.
> 

[1] does soft reset on shutdown which should put it to reset default
state of 1S-1S-1S mode (if thats the POR default)

But, there is still one open question now that we are considering
supporting stateful modes:

What to do with flashes that power up in 8D mode either due to factory
defaults or if 8D mode NV bit is set? Do we say SPI NOR framework won't
support such flashes?
Auto discovery of such flashes is quite difficult as different flashes
use different protocols for RDID cmd in 8D mode (address phase may or
may not be present, dummy cycles vary etc) is almost impossible w/o any
hint passed to the driver?

> Regards,
> 
> Boris
> 
> [1]https://lkml.org/lkml/2020/3/13/659
> 