Re: Xen on RP4

[Julien Grall <julien@xxxxxxx>]

Hi Elliott,

On 24/10/2020 06:35, Elliott Mitchell wrote:
> On Fri, Oct 23, 2020 at 04:59:30PM -0700, Stefano Stabellini wrote:
> > Note that I tried to repro the issue here at my end but it works for me
> > with device tree. So the swiotlb_init memory allocation failure probably
> > only shows on ACPI, maybe because ACPI is reserving too much low memory.
> Found it.  Take a look at 437b0aa06a014ce174e24c0d3530b3e9ab19b18b
>
>   PLATFORM_START(rpi4, "Raspberry Pi 4")
>       .compatible     = rpi4_dt_compat,
>       .blacklist_dev  = rpi4_blacklist_dev,
> +    .dma_bitsize    = 30,
>   PLATFORM_END
>
> Where this is used to match against a *device-tree*.
Right. When we introduced ACPI in Xen, we made the assumption there 
would be no need for per-platform workaround.
> ACPI has a distinct
> means of specifying a limited DMA-width; the above fails, because it
> assumes a *device-tree*.
Do you know if it would be possible to infer from the ACPI static table 
the DMA-width?
If not, is there a way to uniquely identify the platform?


Cheers,

--
Julien Grall