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

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Date:	Tue, 12 Feb 2013 07:56:41 -0800
From:	Vinod Koul <vinod.koul@...el.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.jf.intel.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.jf.intel.com>,
	linux-kernel@...r.kernel.org, spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCH] dw_dmac: adjust slave_id accordingly to request line
 base

On Wed, Jan 30, 2013 at 09:32:56AM +0200, Andy Shevchenko wrote:
> On Tue, 2013-01-29 at 20:57 +0530, Viresh Kumar wrote: 
> > On Tue, Jan 29, 2013 at 10:52 AM, Mika Westerberg
> > <mika.westerberg@...ux.intel.com> wrote:
> > > We had a discusssion about this with Andy as well. The thing is that there
> > > is no way in current resource to pass DMA request line numbers supported by
> > > the controller to the driver in a generic way. We on the other hand have to
> > > deal this somehow as we have a shared DMA controller on Lynxpoint where the
> > > offset will start from 16 (but it might be something else as well).
> > >
> > > Is there something which limits the usage of IORESOUCE_DMA to be only
> > > usable for ISA DMA channels?
> > 
> > Andy,
> > 
> > Why do we need this request_line_base? Why not program the actual value
> > directly into the slave structure (base + offset)?
> 
> Slave device exactly has knowledge about this number slave_id = (base
> +offset). However...
Btw request line needs to be programmed by client in slave_id field.
So why exactly is this required for dma driver?

--
~Vinod
> > In case it is required, add it in platform data field or can add DT
> > binding for it.
> 
> We get a device from the ACPI CSRT table. During enumeration we don't
> know what kind of the device it is. From the enumeration point of view
> each device enumerated from CSRT is a platform device (see
> drivers/acpi/csrt.c for the details).
> 
> That's why we have to pass this info somehow to the DMAC driver. And
> like Mika already mentioned we have no other generic way except
> IORESOURCE_DMA. If you have something better in mind, please share. We
> could adopt our code then.
> 
> 
> -- 
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Intel Finland Oy
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