Re: [Xen-devel] [XEN PATCH v1] libxl: Add DTB compatible list to config file

[Oleksandr <olekstysh@xxxxxxxxx>]

On 16.10.19 18:04, Julien Grall wrote:
> Hi,
Hi Julien


just my 2 cents)


> > Below is example from linux kernel sources:
> >
> > linux/sound/ppc/awacs.c:741:    if 
> > (of_machine_is_compatible("PowerBook3,1")
> > linux/sound/ppc/awacs.c:742:        ||
> > of_machine_is_compatible("PowerBook3,2")) {
> > linux/sound/ppc/awacs.c:770:#define IS_PM7500
> > (of_machine_is_compatible("AAPL,7500") \
> > linux/sound/ppc/awacs.c:771:        || 
> > of_machine_is_compatible("AAPL,8500") \
> > linux/sound/ppc/awacs.c:772:        || 
> > of_machine_is_compatible("AAPL,9500"))
> > ...
> > linux/arch/arm/mach-omap2/pdata-quirks.c:703:        if
> > (of_machine_is_compatible(quirks->compatible)) {
> > linux/arch/arm/mach-omap2/pdata-quirks.c:717:    if
> > (of_machine_is_compatible("ti,omap2420") ||
> > linux/arch/arm/mach-omap2/pdata-quirks.c:718:
> > of_machine_is_compatible("ti,omap3"))
> > linux/arch/arm/mach-omap2/pdata-quirks.c:721:    if
> > (of_machine_is_compatible("ti,omap3"))
> > ...
> >
> > Also see [1]
> >
> > [1] 
> > https://source.codeaurora.org/external/imx/imx-xen/commit/?h=imx_4.14.98_2.0.0_ga&id=6e58d478203639e71da3da69ffeae3fa5dc0197b
> So this is a grep from Linux, I have already done that. What I am 
> looking at is an exact description of your problem. Can you tell me 
> what you are trying to passthrough? Can you also provide a pointer to 
> the Linux code checking the compatible for your problem?
I have no idea whether it is ok or not to pass machine/SoC compatible to 
a guest from the safety PoV, so I am not going to comment regarding safety.
I just would like to provide description of the problem we could face 
when not passing machine/SoC compatible to a guest which runs real H/W 
(not PV) devices.
...

I have just checked without passing real "dt_compatible" to a guest on 
the M3N board. So, this can be considered as real example.
I noticed that at least two H/W devices (which are pass throughed to the 
guest) suffered from the lack of compatible: sdhi_internal_dmac and 
xhci-hcd. And as result SD card and USB host are not functional.
Why this happened? There is SoC Identification framework which purpose 
is to detect SoC's id/revision for the future use in drivers to properly 
apply some quirks (if needed). And without real compatible string in 
place the framework fails
to proceed leaving the SoC attributes unregistered [1]. This results in 
SDHI Internal DMAC controller fails to identify the SoC [2], so can't 
operate.
I didn't investigate what is wrong with the xHCI, but I tend to think 
that the problem is close to what we have with the SDHI.
[1] 
https://elixir.bootlin.com/linux/v5.4-rc2/source/drivers/soc/renesas/renesas-soc.c#L292
[2] 
https://elixir.bootlin.com/linux/v5.4-rc2/source/drivers/mmc/host/renesas_sdhi_internal_dmac.c#L328

--
Regards,

Oleksandr Tyshchenko


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