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Date: Tue, 30 Jan 2024 09:51:41 +0200
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Subject: Re: [PATCH v2] mmc: renesas_sdhi: Fix change point of data handling
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To: Wolfram Sang <wsa+renesas@sang-engineering.com>, ulf.hansson@linaro.org,
 takeshi.saito.xv@renesas.com, masaharu.hayakawa.ry@renesas.com,
 yoshihiro.shimoda.uh@renesas.com, linux-mmc@vger.kernel.org,
 linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
References: <20240117110646.1317843-1-claudiu.beznea.uj@bp.renesas.com>
 <ZbeEPg1jc5qWJa5m@ninjato> <345bc392-cf28-479a-9453-5bc89f635759@tuxon.dev>
 <ZbikovLbujyGS1ub@ninjato>
From: claudiu beznea <claudiu.beznea@tuxon.dev>
In-Reply-To: <ZbikovLbujyGS1ub@ninjato>
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On 30.01.2024 09:26, Wolfram Sang wrote:
> Hi Claudiu,
> 
>> My understanding was the other way around from this statement found in
>> RZ/G3S hw manual:
>>
>> "If all of the TAP [i] is OK, the sampling clock position is selected by
>> identifying the change point of data.
> 
> Yes, it is easy to misunderstand. It should add "and avoid it" or
> something. I got an internal diagram which makes it more clear. I just
> asked if I can share it with you.
> 
>>> I also have a chapter named like this. If you check the diagram, change
>>> point is between TAP2 and 3, so the suggested TAP to use is 6 or 7. As
>>> far away as possible from the change point.
>>
>> My understanding was different here as of the following hw manual statement:
>>
>> "As the width of the input data is 1 (UI), select TAP6 or TAP7 which is
>>
>> *the median* of next TAP3 from TAP3"
>>
>> I understand from this that the median value should be considered here.
> 
> Sorry, can't follow you here. "Select TAP6 or TAP7" is clear to me. But
> it doesn't really matter why it was misleading...
> 
>>> However, with some SD cards, I also see the EIO error you see. So, there
>>> might be room to improve TAP selection when all TAPs are good. I need to
>>> check if this is really is the same case for the SD cards in question.
>>
>> Maybe better would be to change this condition:
>>
>> 			if (cmpngu_data != cmpngd_data)
>> 				set_bit(i, priv->smpcmp);
>>
>> like this:
>> 			if (cmpngu_data == cmpngd_data)
>> 				set_bit(i, priv->smpcmp);
>>
>> ?
>>
>> I need to check it, though.
> 
> But isn't it equal to the current code then? (Except for one thing: the

From my debugging session I remember the SMPCMP was not zero and this lead
to my failure.

I'm not sure (and I don't remember from my debugging session) if CMPNGU and
CMPNGD are identical after the change point of the input data (CMPNGU  !=
CMPNGD) has been signaled by the controller. I need to check it.

> smpcmp bit is only set when there is no cmd error. I need to double
> check but I think I like that.)
> 
> Happy hacking,
> 
>    Wolfram
>