linux-kernel - Re: [PATCH v2 0/4] mtd: pxa3xx

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Date:	Tue, 04 Aug 2015 18:56:23 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	zmxu@...vell.com, jszhang@...vell.com,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	"linux-mtd\@lists.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] mtd: pxa3xx_nand: rework the timing setup

Ezequiel Garcia <ezequiel@...guardiasur.com.ar> writes:

>>
>> The issue I see is that :
>>  - there is a bug in the clk driver for pxa3xx I introduced (CKEN_AB)

>>  - and shutting down the GCU clock prevents the NAND from working (I can't
>>  explain that one yet)

Ah actually it's even trickier, but it has nothing to do with the GCU clock,
that was a wrong interpretation of the test sequence.

What actually happens is that on the platform I have, the NAND is sharing the
DFI bus with the Static Memory Controller. Now let's see what happens on
boot-up, knowing that my pxa3xx-nand is a module, not builtin :
 - the kernel boots
 - the core clock initializes
 - the ethernet card initializes (it is on the static memory controller)
 - the kernel finishes the boot sequence
   => the NAND clock is unused
   => as such, the core clock framework disables it

And here is the catch : on the next ethernet access, the system bus will be
stalled forever. The reason behind is that because the bootloader left the
"NDCR_ND_ARB_EN" bit enabled, the DFI bus sees the ethernet register access, and
asks for arbitration; as the NAND clock is down, the arbitration never happens,
and the pxa3xx is stalled forever.

The very same thing happens when you load and unload pxa3xx-nand with a platform
where it was loaded with "enable-arbiter" platform-data, and if that platform
has any driver mapped in the SMC address space (0x0 .. 0x14000000).

If you have an opportunity to load/unload a pxa3xx-nand, I'd be glad to have
someone verify this theory.

The first fix comming to my mind would be to :
 - disable the NDCR_ND_ARB_EN in the pxa3xx core bring up
 - keep enablement in pxa3xx-nand
 - ensure it is disabled on the probe error path or remove of pxa3xx-nand

Cheers.

--
Robert

PS: That also means that the fix I posted for CKENA/CKENB inversion should fix
the issues you see.
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