Re: [PATCH] mtd: rawnand: qcom: update last code word register
From: mdalam
Date: Wed Feb 24 2021 - 11:36:59 EST
On 2021-02-24 12:18, Miquel Raynal wrote:
Hello,
mdalam@xxxxxxxxxxxxxx wrote on Wed, 24 Feb 2021 10:09:48 +0530:
On 2021-02-24 01:13, mdalam@xxxxxxxxxxxxxx wrote:
> On 2021-02-23 22:04, Miquel Raynal wrote:
>> Hello,
>> >> Md Sadre Alam <mdalam@xxxxxxxxxxxxxx> 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.
Below is the mapping example for a 2K page size.
<---------------------2048------------------------------------------------><------64---------->2111
_______________________________________________________________________________________________
|
| | |
|
| | |
|
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|
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|__________________________________________________________________________|___|_______________|
2048-bytes
factory BBM
One code word:
1-byte BBM 7-bytes ECC
______________________________________
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
|____________|__|____________|___|____|
<-----------512 bytes-------> 4-bytes spare
data
<-------------------------------------2048-------------------------------------------------->2047<------64---------->2111
____________________________________________________________________________________________________________________
|
| | | |
|
| | | |
|
| | | |
|
| | | |
|_____________________________________________________________________________________________|___|_____________|____|
| |
| |
| |<-----mapping
| |
| |
____________________________________________________________________________________________________|___|______
| | |
| |
| | |
| |
| | |
| |
| | |
| |
| | |
| |
|______________________|___________________________|_______________________________|____________________________|
<-------CW1-----------><----------CW2-------------><-----------CW3----------------><----------CW4--------------->
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
_________________________________________________________________ \___
|
|
|
|
|
|
|
|
|
|
|
|
|<--read_location_0--> <---read_location_1-->
<--read_location_n-->|
|
|_____________________________________________________________________|
So in QPIC V2 onwards to access last code word same way we have to use
read_location_last_0,1,2..3 etc.
So whether we are having 4 code words
or 8 code words it doesn't matter. If we wanted access the location
within normal code word we have to
use READ_LOCATION register and if we wanted to access location in
last code word then we have to use
READ_LOCATION_LAST.
>
>> >>> Signed-off-by: Md Sadre Alam <mdalam@xxxxxxxxxxxxxx>
Thanks,
Miquèl