linux-kernel - Re: [RFC PATCH 2/4] mmc: core: implement enhanced strobe support

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Date:	Fri, 4 Mar 2016 10:00:52 +0800
From:	Shawn Lin <shawn.lin@...nel-upstream.org>
To:	Adrian Hunter <adrian.hunter@...el.com>,
	Shawn Lin <shawn.lin@...k-chips.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Michal Simek <michal.simek@...inx.com>,
	soren.brinkmann@...inx.com, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/4] mmc: core: implement enhanced strobe support

Hi Adrian,

On 2016/3/3 21:37, Adrian Hunter wrote:
> On 03/03/16 04:36, Shawn Lin wrote:
>> Controllers use data strobe line to latch data from devices
>> under hs400 mode, but not for cmd line. So from emmc 5.1, JEDEC
>> introduces enhanced strobe mode for latching cmd response from
>> emmc devices to host controllers. This new feature is optional.
>
> As I currently understand it, HS400ES does not require tuning.
> Consequently you can go straight to HS400ES and do not need to do
> HS200 first.  If that is the case then more changes are needed.
>

That's the case, and it's already in my plan before I going to remove
"RFC" prefix. From my experience of developing emmc-device firmware, the
only reason we need tuning for HS200 before we switch it into HS400
is that although data-line can be latched by DS but the cmd-line is 
still in SDR mode when runing in HS400. With hs400-es setuped, tuning
and retune stuff is meaningless. ALl the SI should be guranteed by HW
design to regulate the PCB payload.

> Also it would be nice if the transfer mode displayed reflected enhanced
> strobe e.g.

Great idea! And maybe more thing should be done for core/debugfs.c
It seems to big change for init_card, so I need more time to split my
step for changing it to make the change will not do any side effect from
non-hs400es procedure. :)

Thanks.

>
> 	Currently
>
> 		mmc1: new HS400 MMC card at address 0001
>
> 	Change for enhance strobe supported
>
> 		mmc1: new HS400ES MMC card at address 0001
>
>
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