linux-kernel - Re: [PATCH] dw_dmac: adjust slave_id accordingly to request line base

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Message-ID: <20130212190236.GD20771@intel.com>
Date:	Tue, 12 Feb 2013 21:02:36 +0200
From:	Mika Westerberg <mika.westerberg@...el.com>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.jf.intel.com>,
	linux-kernel@...r.kernel.org,
	spear-devel <spear-devel@...t.st.com>,
	Mika Westerberg <mika.westerberg@...ux.jf.intel.com>
Subject: Re: [PATCH] dw_dmac: adjust slave_id accordingly to request line base

On Tue, Feb 12, 2013 at 09:34:35AM -0800, Vinod Koul wrote:
> On Tue, Feb 12, 2013 at 06:43:51PM +0200, Mika Westerberg wrote:
> > On Tue, Feb 12, 2013 at 07:53:34AM -0800, Vinod Koul wrote:
> > > On Tue, Jan 29, 2013 at 10:29:43AM +0530, Viresh Kumar wrote:
> > > > Next time, please direct these mails to my Linaro id :)
> > > > 
> > > > On Mon, Jan 28, 2013 at 4:34 PM, Andy Shevchenko
> > > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > > > On some hardware configurations we have got the request line with the offset.
> > > > > The patch introduces convert_slave_id() helper for that cases. The request line
> > > > > base is got from the platform device resources provided by the IORESOURCE_DMA
> > > > > type.
> > > > 
> > > > @Vinod: Is IORESOURCE_DMA suitable for this purpose?
> > > Looks unlikely...
> > > 
> > > But why do we need this in first place?
> > > 
> > > I know this is due to common platform probe. Clearly one size not fitting all.
> > > If you had dedicated PCI probe you wouldnt worrry right?
> > 
> > This is all related to new ACPI 5.0 features for devices enumerated from
> > ACPI namespace, such as SPI controller.
> > 
> > ACPI 5.0 allows BIOS to specify DMA request lines and channels used by a
> > slave device with FixedDMA() descriptors, such as:
> > 
> > 	FixedDMA (0x0010, 0x0000, Width32bit,) // TX
> > 	FixedDMA (0x0011, 0x0001, Width32bit,) // RX
> > 
> > The first field (0x10, 0x11) is the request line assigned to the device. In
> > this particular case it is the SPI controller.
> > 
> > Now there is only one DMA controller in this platform but the request lines
> > still start from 0x10 (16).
> > 
> > Then there is another ACPI table called CSRT (Core System Resources Table)
> > that assings request line range to the DMA controller itself. This range
> > starts from 0x10 (16) for this platform.
> > 
> > So what we do is that we parse this CSRT table, create platform device for
> > the DMA controller of found and pass the request line range as
> > IORESOURCE_DMA resource with the platform device.
> Okay, who parses the CSRT table and how is this presented to OS.

ACPI code, found under drivers/acpi/csrt.c handles this. Note that this
code is heading 3.9 so it is not in mainline yet but available in
linux-pm.git/linux-next branch. I can dig the commit id if you are
interested.

> Can we do this in platform data and complete the base calculation.

Do you mean platform data for the dmac driver?

The CSRT parser code can't know what the platform data requirements for the
particular dmac driver are. It only creates the platform devices and adds
MMIO, IRQ and possible DMA resources. It is up to the (dmac) driver to use
this information for whatever purposes in needs.

> In ACPI 5, is DMA a PCI device or platfrom device?

It is platform device.
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