Re: Problems when using latest git tree to boot xen on OMAP5

[Chen Baozi <baozich@gmail.com>]

On Wed, Oct 09, 2013 at 09:11:16AM +0100, Ian Campbell wrote:
> On Wed, 2013-10-09 at 15:46 +0800, Chen Baozi wrote:
> > On Mon, Oct 07, 2013 at 11:59:16AM +0100, Julien Grall wrote:
> > > On 10/07/2013 10:58 AM, Chen Baozi wrote:
> > > > On 10/07/2013 04:39 PM, Ian Campbell wrote:
> > > >>
> > > >> It is certainly a bug in the kernel if it is accessing something which
> > > >> is disabled. It may also independently be a bug in the dts that this
> > > >> devices is disabled.
> > > >>
> > > >> However in v3.12-rc4 I don't see mmc@480d1000 being disabled in
> > > >> omap5-uevm.dts and I can't see anything in the history of that file
> > > >> either. Where did your copy come from?
> > > > 
> > > > I'm currently working on the "omap5-v3.11-rc3" branch from
> > > > git://github.com/rogerq/linux.git, which contains a few necessary
> > > > platform patches not upstreamed. In omap5-uevm.dts, there are lines like:
> > > > 
> > > > 253 &mmc4 {
> > > > 254     status = "disabled";
> > > > 255 };
> > > > 256
> > > > 257 &mmc5 {
> > > > 258     status = "disabled";
> > > > 259 };
> > > > 
> > > > the mmc4 refers to mmc@480d1000, which defines at omap5.dtsi:
> > > > 
> > > > 417         mmc4: mmc@480d1000 {
> > > > 
> > > > I checked Linus' mainline git tree. It is the same about disabled mmc4
> > > > in omap5-uevm.dts. And the change is introduced in commit 5dd18b0 of the
> > > > mainline kernel.
> > > > 
> > > > Anyway, I'll see what exactly happened in the dom0 kernel dealing with
> > > > those "disabled" regions.
> > > 
> > > I looked at the Linux code. It will populate the different devices via
> > > the of_platform_populate (drivers/of/platform.c).
> > > 
> > > This function checks in of_platform_create_pdata if the device is
> > > available. So the mmc driver (driver/mmc/host/omap_hsmmc.c) should not
> > > be called for mmc4.
> > 
> > I've discuessed this issue on linux-omap@vger.kernel.org. The TI guy says
> > that "DT disabled" means that device won't be created but hwmod bus
> > initially would try to initialize all supported modules by doing reset
> > access in their io memory address regions. That's why dom0 have accessed
> > mmc4 address even though it has been disabled.
> 
> ePAPR lists the option of "status = fail" which is "Indicates that the
> device is not operational. A serious error was detected in the device,
> and it is unlikely to become operational without repair." I'm not sure
> that is quite right though.
> 
> Rather than whitelisting and mapping disabled devices through perhaps we
> should implement them as read 0xf (or 0x0) and write ignore?
> 
> Or maybe we should just be mapping non-blacklisted disabled devices
> through to dom0, for it to use or ignore as it pleases. Julien, what was
> the reasoning here again?

If we just simple don't pass the disabled node in DT to the dom0, anything
inpropriate?

Baozi.