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: Wed, 19 Jul 2023 10:21:53 +0200	[thread overview]
Message-ID: <20230719102153.2ef93cfe@xps-13> (raw)
In-Reply-To: <yw1xy1jdxqot.fsf@mansr.com>

Hi Måns,

mans@mansr.com wrote on Tue, 18 Jul 2023 15:03:14 +0100:

> Miquel Raynal <miquel.raynal@bootlin.com> writes:
> 
> > 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  
> 
> I'm still not sure what exactly you want to me measure.  The waitrdy and
> ndelay combined, each separately, or something else?
> 

I would like to know, how much time we spend waiting in both cases. Is
there something wrong with the "wait ready"? As we cannot observe the
timings with a scope, because we are using a "soft" controller
implementation somehow, we can easily measure how much time we
spend in each operation by measuring the time before and after.

These information are only useful when we are doing operations related
to sequential reads.

Thanks,
Miquèl

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