Re: [PATCH] mmc: sunxi: fix unusuable eMMC on some H6 boards by disabling DDR

From: "Alejandro González" <alejandro.gonzalez.correo@gmail•com>
To: Ulf Hansson <ulf.hansson@linaro•org>,
	Maxime Ripard <maxime.ripard@bootlin•com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
	Linus Walleij <linus.walleij@linaro•org>,
	linux-sunxi <linux-sunxi@googlegroups•com>,
	"linux-mmc@vger•kernel.org" <linux-mmc@vger•kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger•kernel.org>,
	Chen-Yu Tsai <wens@csie•org>,
	Thomas Gleixner <tglx@linutronix•de>,
	Linux ARM <linux-arm-kernel@lists•infradead.org>
Subject: Re: [PATCH] mmc: sunxi: fix unusuable eMMC on some H6 boards by disabling DDR
Date: Wed, 28 Aug 2019 12:52:49 +0200	[thread overview]
Message-ID: <f84d62b7-da00-f2bd-36e9-972435080bfe@gmail.com> (raw)
In-Reply-To: <CAPDyKFr5opD2yBXmFRBY-9oA_3ShVv0GPFRO8Q_8TEiT+z2pQA@mail.gmail.com>

El 27/8/19 a las 15:24, Ulf Hansson escribió:> Assuming this should go stable as well? Perhaps you can find a
> relevant commit that we can put as a fixes tag as well?
> 
> Kind regards
> Uffe

The most relevant commit I've found that is related to enabling DDR speeds
on H6 boards is this one: https://github.com/torvalds/linux/commit/07bafc1e3536a4e3c422dbd13341688b54f159bb .
But it doesn't address the H6 SoC specifically, so I doubted whether it would
be appropiate to mark this patch as fixing it, and opted to not do it. I don't
mind adding that tag if it's appropiate, though :-)

On the other hand, I'm not sure that I understood correctly what do you mean by
this patch going stable, but I might say the changes themselves are stable and work.
The only downside I can think of to them is that they are a kind of workaround that
reduces performance on H6 boards and/or eMMC not affected by this problem (are there
any?), unless device trees are changed.

El 27/8/19 a las 15:32, Maxime Ripard escribió:
> On Sun, Aug 25, 2019 at 05:05:58PM +0200, Alejandro González wrote:
>> Some Allwinner H6 boards have timing problems when dealing with
>> DDR-capable eMMC cards. These boards include the Pine H64 and Tanix TX6.
>>
>> These timing problems result in out of sync communication between the
>> driver and the eMMC, which renders the memory unsuable for every
>> operation but some basic commmands, like reading the status register.
>>
>> The cause of these timing problems is not yet well known, but they go
>> away by disabling DDR mode operation in the driver. Like on some H5
>> boards, it might be that the traces are not precise enough to support
>> these speeds. However, Jernej Skrabec compared the BSP driver with this
>> driver, and found that the BSP driver configures pinctrl to operate at
>> 1.8 V when entering DDR mode (although 3.3 V operation is supported), while
>> the mainline kernel lacks any mechanism to switch voltages dynamically.
>> Finally, other possible cause might be some timing parameter that is
>> different on the H6 with respect to other SoCs.
> 
> This should be a comment in the driver where this is disabled.
> 
> Maxime

Thank you for your review. I'll mention that briefly in a comment in the code for
the next revision of this patch.

Regards.

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