Re: amba pl011: where to submit a fix for x86 builds

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Fri, Jun 07, 2013 at 11:38:54AM +0200, Alessandro Rubini wrote:
> Hello.
> This is cc'd to $(get_maintainer.pl -f drivers/tty/serial/amba-pl011.c)
> and x86 maintainers too.
> 
> While working on the pci-to-amba bridge driver (to be resubmitted in
> the next days) I have to deal with the problem of pl011 not building,
> after phys_to_page was introduced, by Chanho Min (Cc: here) in commit
> 
>    cb06ff1 ARM: PL011: Add support for Rx DMA buffer polling.
> 
> because x86 has no phys_to_page.
> 
> The fix I use is trivially this:
> 
>   -       sg_set_page(&sg->sg, phys_to_page(dma_addr),
>   +       sg_set_page(&sg->sg, virt_to_page(sg->buf),
> 
> (virt_to_page is slower, but other sg_get_page() users do the same
> and other solutions are more convoluted).

... and thereby breaks ARM, because sg->buf is not part of the kernel
direct mapped RAM region.

I don't think there's a portable way to do the above, because the DMA
coherent API doesn't really support translating the allocated memory
region to a struct page pointer.