linux-kernel - Re: [PATCH] mtd: rawnand: qcom: update last code word register

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Message-ID: <92fc28e79b5f6f56c8bfc6f229807edb@codeaurora.org>
Date:   Fri, 26 Feb 2021 23:55:53 +0530
From:   mdalam@...eaurora.org
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     mani@...nel.org, boris.brezillon@...labora.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        sricharan@...eaurora.org, mdalam=codeaurora.org@...eaurora.org
Subject: Re: [PATCH] mtd: rawnand: qcom: update last code word register

On 2021-02-24 22:06, Miquel Raynal wrote:
> Hello,
> 
> mdalam@...eaurora.org wrote on Wed, 24 Feb 2021 22:00:05 +0530:
> 
>> On 2021-02-24 12:18, Miquel Raynal wrote:
>> > Hello,
>> >
>> > mdalam@...eaurora.org wrote on Wed, 24 Feb 2021 10:09:48 +0530:
>> >
>> >> On 2021-02-24 01:13, mdalam@...eaurora.org wrote:
>> >> > On 2021-02-23 22:04, Miquel Raynal wrote:
>> >> >> Hello,
>> >> >> >> Md Sadre Alam <mdalam@...eaurora.org> wrote on Tue, 23 Feb 2021
>> >> >> 01:34:27 +0530:
>> >> >> >>> From QPIC version 2.0 onwards new register got added to read last
>> >> >> >>                                a new
>> >> >> >>> codeword. This change will add the READ_LOCATION_LAST_CW_n register.
>> >> >> >>             Add support for this READ_LOCATION_LAST_CW_n register.
>> >> >> >>> >>> For first three code word READ_LOCATION_n register will be
>> >> >>> use.For last code word READ_LOCATION_LAST_CW_n register will be
>> >> >>> use.
>> >> >> >> "
>> >> >> In the case of QPIC v2, codewords 0, 1 and 2 will be accessed through
>> >> >> READ_LOCATION_n, while codeword 3 will be accessed through
>> >> >> READ_LOCATION_LAST_CW_n.
>> >> >> "
>> >> >> >> When I read my own sentence, I feel that there is something wrong.
>> >> >> If there are only 4 codewords, I guess a QPIC v2 is able to use
>> >> >> READ_LOCATION_3 or READ_LOCATION_LAST_CW_0 interchangeably. Isn't it?
>> >> >> >> I guess the point of having these "last_cw_n" registers is to support
>> >> >> up to 8 codewords, am I wrong? If this the case, the current patch
>> >> >> completely fails doing that I don't get the point of such change.
>> >> >
>> >> > This register is only use to read last code word.
>> >> >
>> >> > I have address all the comments from all the previous sub sequent
>> >> > patches and pushed
>> >> > all patches in only one series.
>> >> >
>> >> > Please check.
>> >> >>   The registers READ_LOCATION & READ_LOCATION_LAST are not associated >> with number of code words.
>> >>   These two registers are used to access the location inside a code >> word.
>> >
>> > Ok. Can you please explain what is a location then? Or point me to a
>> > datasheet that explains it.
>> 
>>    The location is the position inside a code word.
>> 
>> >
>> > Bottom line question: why having READ_LOCATION_0, _1,... an
>> > READ_LOCATION_LAST_0, _1, etc?
>> 
>>   READ_LOCATION_0, _1,... are used to extract multiple chunks from a 
>> code word.
>> 
>>   e.g If we wanted to extract first 100 bytes from a code word then 
>> (0...99) READ_LOCATION_0 will be configured.
>>       if we wanted to extract next 100 bytes (100...199) then 
>> READ_LOCATION_1 will be configured.
>> 
>>       same way for last code word READ_LOCATION_LAST_0, _1, will be 
>> used.
>> 
> 
> Nice explanation, and thanks for the below figures. So I guess there
> is some kind of "small SRAM" that is
> directly addressable perhaps?
> 
> I think I'm fine with your series now. Just a small nit: next time you
> send a series, please update the version number "[PATCH v6]"
> (automatically added with the -v6 parameter in git-format-patch). But
> no need to resend just for that.
> 

   Thanks Miquel. So now no need to test these patches further. I have 
already tested these patches on IPQ5018 SoC with mtd_test module & 
nand-utils tool.

> 
> Thanks,
> Miquèl