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

[Måns Rullgård]

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

> Hi Måns,
>
> mans at mansr.com wrote on Wed, 19 Jul 2023 10:26:09 +0100:
>
>> Miquel Raynal <miquel.raynal at bootlin.com> writes:
>> 
>> > Hi Måns,
>> >
>> > mans at mansr.com wrote on Tue, 18 Jul 2023 15:03:14 +0100:
>> >  
>> >> Miquel Raynal <miquel.raynal at bootlin.com> writes:
>> >>   
>> >> > Hi Måns,
>> >> >
>> >> > mans at mansr.com wrote on Mon, 17 Jul 2023 14:11:31 +0100:
>> >> >    
>> >> >> Miquel Raynal <miquel.raynal at 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?
>
> ndelay and more importantly, waitrdy:

[...]

>> > 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.
>
> Great. The only issue with the scope is the fact that we might actually
> look at something that is not a faulty sequential read op.

How exactly do I know which ones are faulty?

> Unless you hack into the core to perform these in a loop (with a
> brutal "while (1)"). But I don't think we require big precision here,
> at least as a first step, looking at software timestamps like hinted
> above is enough so we can easily identify the different delays and
> compare them with nand_timings.c.
>
> Please use whatever method is easier for you.

Which values should be compared?

Sorry if I'm being obtuse, I don't normally have to deal with these
things.

-- 
Måns Rullgård