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

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Date:   Wed, 24 Feb 2021 17:36:44 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     mdalam@...eaurora.org
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

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,
Miquèl