Re: RZ/G2M Hangs when booting some SD cards

From: Wolfram Sang <wsa+renesas@sang-engineering.com>
To: Adam Ford <aford173@gmail.com>
Cc: linux-mmc <linux-mmc@vger.kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>
Subject: Re: RZ/G2M Hangs when booting some SD cards
Date: Wed, 31 May 2023 08:51:19 +0200	[thread overview]
Message-ID: <ZHbuZyuQ+uZKul+c@ninjato> (raw)
In-Reply-To: <CAHCN7xLLsXikG=8zSM=udqnqwvbkqkSLH8iYcuLiLVvHa=LPPQ@mail.gmail.com>

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Hi Adam,

I am very sorry that it took so long until I am now able to respond.
First, too many other duties with higher priority came in. Second, the
card didn't fail 100% for me after all which made debugging still
challenging. But it failed often enough, so I at least have a pointer
now.

> From what I have been able to determine, the U-Boot code explicitly
> disables DMA during the tuning phase:

...

> However, Linux does not disable the DMA, and the value of taps is zero
> and the tuning ultimately fails.

I disabled DMA while tuning but it did not help. It finally turns out
that adding a delay after each tuning command seems to help. U-Boot does
this but Marek (the driver author for U-Boot) cannot recall why he added
the delay. I'll send a patch in some minutes.

All the best,

   Wolfram

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