Re: [PATCH v2 3/3] mtd: rawnand: Support for sequential cache reads

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: "Måns Rullgård" <mans@mansr.com>
Cc: Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Tudor Ambarus <Tudor.Ambarus@microchip.com>,
	Pratyush Yadav <pratyush@kernel.org>,
	Michael Walle <michael@walle.cc>, <linux-mtd@lists.infradead.org>,
	Julien Su <juliensu@mxic.com.tw>,
	Jaime Liao <jaimeliao@mxic.com.tw>,
	Alvin Zhou <alvinzhou@mxic.com.tw>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	JaimeLiao <jaimeliao.tw@gmail.com>,
	Alexander Shiyan <eagle.alexander923@gmail.com>,
	Domenico Punzo <dpunzo@micron.com>, Bean Huo <beanhuo@micron.com>
Subject: Re: [PATCH v2 3/3] mtd: rawnand: Support for sequential cache reads
Date: Mon, 17 Jul 2023 18:36:45 +0200	[thread overview]
Message-ID: <20230717183645.32ef90b0@xps-13> (raw)
In-Reply-To: <yw1x351mznr0.fsf@mansr.com>

Hi Måns,

mans@mansr.com wrote on Mon, 17 Jul 2023 14:11:31 +0100:

> Miquel Raynal <miquel.raynal@bootlin.com> writes:
> 
> > So, I should have done that earlier but, could you please slow the
> > whole operation down, just to see if there is something wrong with the
> > timings or if we should look in another direction.
> >
> > Maybe you could add a boolean to flag if the last CMD was a
> > READCACHESEQ, READCACHESTART or READCACHEEND, and if the flag is
> > true, please get the jiffies before and after each waitrdy and
> > delay_ns. Finally, please print the expected delay and the actual one
> > and compare to see if something was too fast compared to what we
> > expected.  
> 
> Between which points exactly should the delay be measured?  Also, there
> is no command called READCACHESTART.  Did you mean READSTART or
> something else?

Yeah, whatever command is specific to sequential cache reads:
https://elixir.bootlin.com/linux/latest/source/drivers/mtd/nand/raw/nand_base.c#L1218
https://elixir.bootlin.com/linux/latest/source/drivers/mtd/nand/raw/nand_base.c#L1228

> > In a second test, you could simply add a udelay(50); at the end of
> > omap_nand_exec_instr().  
> 
> That didn't help.

Really? That's disappointing (thanks a lot for your quick feedback).

Let's see what the measurements will return.

Thanks,
Miquèl

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