linux-kernel - Re: [PATCH v2] mtd: nand: raw: atmel: Respect tAR, tCLR in read setup timing

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Message-ID: <20250825-vista-cuddle-c159a6bd97ec@thorsis.com>
Date: Mon, 25 Aug 2025 15:22:29 +0200
From: Alexander Dahl <ada@...rsis.com>
To: "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>
Cc: "Balamanikandan.Gunasundar@...rochip.com" <Balamanikandan.Gunasundar@...rochip.com>,
	"miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
	"claudiu.beznea@...on.dev" <claudiu.beznea@...on.dev>,
	"nicolas.ferre@...rochip.com" <nicolas.ferre@...rochip.com>,
	"richard@....at" <richard@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"vigneshr@...com" <vigneshr@...com>,
	"alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"bbrezillon@...nel.org" <bbrezillon@...nel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] mtd: nand: raw: atmel: Respect tAR, tCLR in read
 setup timing

Hello Alexander,

Am Mon, Aug 25, 2025 at 12:21:24PM +0000 schrieb Sverdlin, Alexander:
> Hi Alexander,
> 
> On Mon, 2025-08-25 at 13:02 +0200, Alexander Dahl wrote:
> > > Having setup time 0 violates tAR, tCLR of some chips, for instance
> > > TOSHIBA TC58NVG2S3ETAI0 cannot be detected successfully (first ID byte
> > > being read duplicated, i.e. 98 98 dc 90 15 76 14 03 instead of
> > > 98 dc 90 15 76 ...).
> > > 
> > > Atmel Application Notes postulated 1 cycle NRD_SETUP without explanation
> > > [1], but it looks more appropriate to just calculate setup time properly.
> > > 
> > > [1] Link: https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/ApplicationNotes/ApplicationNotes/doc6255.pdf
> > > Cc: stable@...r.kernel.org
> > > Fixes: f9ce2eddf176 ("mtd: nand: atmel: Add ->setup_data_interface() hooks")
> > > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> > 
> > Tested-by: Alexander Dahl <ada@...rsis.com>
> > 
> > Threw this on top of 6.12.39-rt11 and tested on two custom platforms
> > both with a Spansion S34ML02G1 SLC 2GBit flash chip, but with
> > different SoCs (sama5d2, sam9x60).  We had difficulties with the
> > timing of those NAND flash chips in the past and I wanted to make sure
> > this patch does not break our setup.  Seems fine in a quick test,
> > reading and writing and reading back is successful.
> 
> thank you for your feedback!
> 
> Do you see an opportunity to drop the downstream timing quirks with my patch?

Which downstream do you refer to?

> I actually have another patch related to timings, but it's based on code-review
> only and the theoretical issue never manifested itself in practice on our side...

I also have another one, for which fixes got merged in at91bootstrap
and U-Boot already, but I never found the time to upstream it on
Linux.  It's related to pulse timing.

> (it's about missing ndelay at the end of atmel_smc_nand_exec_instr())

That does not ring a bell here, sorry.

Greets
Alex