linux-kernel - Re: [PATCH 6/8] ARM: mvebu: enable SDHCI card detection using DAT3 pin on A388-GP

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Message-ID: <8737xo9gvx.fsf@free-electrons.com>
Date:	Tue, 06 Oct 2015 17:05:38 +0200
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	Marcin Wojtas <mw@...ihalf.com>, Andrew Lunn <andrew@...n.ch>
Cc:	linux-kernel@...r.kernel.org,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-mmc\@vger.kernel.org" <linux-mmc@...r.kernel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	nadavh@...vell.com, Lior Amsalem <alior@...vell.com>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Grzegorz Jaszczyk <jaz@...ihalf.com>
Subject: Re: [PATCH 6/8] ARM: mvebu: enable SDHCI card detection using DAT3 pin on A388-GP

Hi,
 
 On mar., oct. 06 2015, Marcin Wojtas <mw@...ihalf.com> wrote:

> Hi Andrew,
>
> 2015-10-06 5:31 GMT+02:00 Andrew Lunn <andrew@...n.ch>:
>> On Tue, Oct 06, 2015 at 03:22:40AM +0200, Marcin Wojtas wrote:
>>> The newest revisions of A388-GP (v1.5 and higher) support only
>>> DAT3-based card detection, which is enabled by this commit. Hitherto
>>> revisions, without such modification, will be impacted with a broken
>>> card detection - in order to operate the cards have to be present
>>> during kernel boot.
>>
>> Humm. Is this acceptable, breaking old boards?
>>
>> I would say at minimum, there should be a big fat comment at the top
>> of armada-388-gp.dts explaining that this DTS file is broken on
>> v0.0-v1.4.
>>
>> Or we have two .dts files for the 388-gp file, and a dtsi file.
>>
>
> I expected this patch would be controversial, hence I propose a
> compromise: set A388-GP SDHCI to 'broken-cd' by defeault. However
> Marvell insisted on HW card detection, because software polling spoils
> the SD/MMC benchmarks, but this way the user would decide whether to
> stay with broken-cd or switch to GPIO/DAT3 detection. What do you
> think?

I don't know hwo to correctly handle this case.

>From my point of view in a ideal work it is typically something that
sould be updated by the bootloader. However in the real world, we can't
rely on the bootloader :(

I also don't like having a dts for each new version of the board but as
the end you can see them as different boards. Also now it seems that the
distribution are moving to link the dtb and the kernel: for eaxh new
version of the kernel they also provide a new version of the dtb. That
means, that if we modify the dts, then the old board won't work with the
new kernel. So maybe creating a armada-388-gp-v1.5.dts could be the best
option.

What do you think of it?

Thanks,

Gregory

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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