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

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Message-ID: <20130607095013.GU18614@n2100.arm.linux.org.uk>
Date:	Fri, 7 Jun 2013 10:50:13 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alessandro Rubini <rubini@...dd.com>
Cc:	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	jslaby@...e.cz, linux-serial@...r.kernel.org, x86@...nel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	Chanho Min <chanho.min@....com>,
	Giancarlo Asnaghi <giancarlo.asnaghi@...com>
Subject: Re: amba pl011: where to submit a fix for x86 builds

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.
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