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

From: "Måns Rullgård" <mans@mansr.com>
To: Miquel Raynal <miquel.raynal@bootlin.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 10:26:09 +0100	[thread overview]
Message-ID: <yw1xttu0xnf2.fsf@mansr.com> (raw)
In-Reply-To: <20230719102153.2ef93cfe@xps-13> (Miquel Raynal's message of "Wed, 19 Jul 2023 10:21:53 +0200")

Miquel Raynal <miquel.raynal@bootlin.com> writes:

> 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.

Which "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.

I have hooked up some spare GPIOs to a scope, which should be more
accurate (nanosecond) than software timestamps.  All I need to know is
what to measure and what to look for in those measurements.

-- 
Måns Rullgård

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