linux-kernel - Re: qemu:beagle no longer booting with omap2plus

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Date:	Sun, 24 Apr 2016 11:10:25 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Roger Quadros <rogerq@...com>,
	Brian Norris <computersforpeace@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: qemu:beagle no longer booting with omap2plus_defconfig in -next

Hi Boris,

On 04/24/2016 10:14 AM, Boris Brezillon wrote:
[ ... ]

>>
>> In qemu, it looks like gpmc bit 0 is considered to be the NAND chip select,
>> which is distinctly different to a chip ready pin.
>
> Well, if you look at the GPIO controller implementation, you'll see
> that gpichip->get() is adding 8 to the GPIO index, so the
> implementation is actually testing bit 8 and not bit 0. Maybe this is
> not emulated properly in qemu though...
>
That helps. The QEMU emulation always returns 0x0001 when reading gpmc register
0x54, which suggests that WAIT0STATUS reports as 0.

>> Guess I would have to try
>> finding a chip datasheet to figure out what this pin is supposed to do, and
>> what is wrong. Since it is somewhat unlikely that I'll find the time to do that,
>> I just disabled MTD_NAND_OMAP2 in my qemu tests instead. Not an ideal solution,
>> of course, but the alternative would be to drop the beagle qemu tests entirely.
>
> Long time I haven't looked at qemu code, but IIRC there were no proper
> support for the NAND layer (maybe this has changed since then though).
> And the R/B pin status emulation is probably much more complicated to
> implement than just returning a valid STATUS byte in a generic NAND chip
> emulation layer (you have to emulate the GPMC block and all its
> external interfaces like the R/B IOs as well as the R/B pin
> emulation at the NAND chip emulation level)...
>

Well enough for it to at least find the NAND chip.

So the qemu "fix" was to return 0x0101 instead of 0x0001 when reading gpmc
register 0x54.

Now I get "INFO: suspicious RCU usage" on reboot, but that is a separate issue.

Thanks a lot for the hints!

Guenter