Re: [PATCH] arm64: iort: take _DMA methods into account for named components

From: Will Deacon <will@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	robin.murphy@arm.com,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm64: iort: take _DMA methods into account for named components
Date: Tue, 28 Apr 2020 18:01:39 +0100	[thread overview]
Message-ID: <20200428170138.GF12697@willie-the-truck> (raw)
In-Reply-To: <CAMj1kXHFJMyw6jYPd9puaN=xc1BYpF7+VnCMkBhMxBgDm9skgg@mail.gmail.com>

On Mon, Apr 20, 2020 at 11:14:50AM +0200, Ard Biesheuvel wrote:
> On Mon, 20 Apr 2020 at 11:13, Lorenzo Pieralisi
> <lorenzo.pieralisi@arm.com> wrote:
> >
> > On Mon, Apr 20, 2020 at 10:58:02AM +0200, Ard Biesheuvel wrote:
> > > On Mon, 20 Apr 2020 at 10:41, Lorenzo Pieralisi
> > > <lorenzo.pieralisi@arm.com> wrote:
> > > >
> > > > On Sat, Apr 04, 2020 at 09:30:47AM +0200, Ard Biesheuvel wrote:
> > > > > Where IORT nodes for named components can describe simple DMA limits
> > > > > expressed as the number of address bits a device can driver, _DMA methods
> > > > > in AML can express more complex topologies, involving DMA translation in
> > > > > particular.
> > > > >
> > > > > Currently, we only take this _DMA method into account if it appears on a
> > > > > ACPI device node describing a PCIe root complex, but it is perfectly
> > > > > acceptable to attach them to named components as well, so let's ensure
> > > > > we take them into account in those cases too.
> > > > >
> > > > > Reported-by: Andrei Warkentin <awarkentin@vmware.com>
> > > > > Fixes: 7ad4263980826e8b ("ACPI: Make acpi_dma_configure() DMA regions aware")
> > > > > Cc: <stable@vger.kernel.org> # v4.14+
> > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > > ---
> > > > >  drivers/acpi/arm64/iort.c | 11 ++++-------
> > > > >  1 file changed, 4 insertions(+), 7 deletions(-)
> > > >
> > > > Only question is whether there is FW in the field with _DMA methods that
> > > > now we would start parsing (and hopefully everything will still work)
> > > > but for that the only choice is applying this patch and see, so:
> > > >
> > >
> > > Perhaps it would be better to call acpi_dma_get_range() on dev->parent then?
> >
> > I think it is fine as it is -  maybe we can hold off sending it all
> > the way to stable kernels until we are confident it does not cause
> > unintended breakage ?
> >
> > Anyway, thanks for putting it together.
> >
> > Minor nit: I'd make "arm64: iort:" in the subject "ACPI/IORT:"
> > just to keep logs uniform.
> >
> 
> OK, I'll respin and resend, with the ACPI folks on cc this time.

Thanks. I'm happy to queue this in the arm64 tree with the CC: stable
dropped for now, so please keep me on cc for v2.

Will

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