linux-kernel - Re: [PATCH 02/13] dmaengine: Introduce dma_request_slave_channel_compat

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Date:	Fri, 12 Jun 2015 18:28:37 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Tony Lindgren <tony@...mide.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	dmaengine@...r.kernel.org,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	linux-crypto@...r.kernel.org,
	linux-spi <linux-spi@...r.kernel.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	ALSA Development Mailing List <alsa-devel@...a-project.org>
Subject: Re: [PATCH 02/13] dmaengine: Introduce
 dma_request_slave_channel_compat_reason()

On Thu, Jun 04, 2015 at 06:58:06PM +0300, Peter Ujfalusi wrote:
> Vinod,
> 
> On 06/02/2015 03:55 PM, Vinod Koul wrote:
> > On Fri, May 29, 2015 at 05:32:50PM +0300, Peter Ujfalusi wrote:
> >> On 05/29/2015 01:18 PM, Vinod Koul wrote:
> >>> On Fri, May 29, 2015 at 11:42:27AM +0200, Geert Uytterhoeven wrote:
> >>>> On Fri, May 29, 2015 at 11:33 AM, Vinod Koul <vinod.koul@...el.com> wrote:
> >>>>> On Tue, May 26, 2015 at 04:25:57PM +0300, Peter Ujfalusi wrote:
> >>>>>> dma_request_slave_channel_compat() 'eats' up the returned error codes which
> >>>>>> prevents drivers using the compat call to be able to do deferred probing.
> >>>>>>
> >>>>>> The new wrapper is identical in functionality but it will return with error
> >>>>>> code in case of failure and will pass the -EPROBE_DEFER to the caller in
> >>>>>> case dma_request_slave_channel_reason() returned with it.
> >>>>> This is okay but am worried about one more warpper, how about fixing
> >>>>> dma_request_slave_channel_compat()
> >>>>
> >>>> Then all callers of dma_request_slave_channel_compat() have to be
> >>>> modified to handle ERR_PTR first.
> >>>>
> >>>> The same is true for (the existing) dma_request_slave_channel_reason()
> >>>> vs. dma_request_slave_channel().
> >>> Good point, looking again, I think we should rather fix
> >>> dma_request_slave_channel_reason() as it was expected to return err code and
> >>> add new users. Anyway users of this API do expect the reason...
> >>
> >> Hrm, they are for different use.dma_request_slave_channel()/_reason() is for
> >> drivers only working via DT or ACPI while
> >> dma_request_slave_channel_compat()/_reason() is for drivers expected to run in
> >> DT/ACPI or legacy mode as well.
> >>
> >> I added the dma_request_slave_channel_compat_reason() because OMAP/daVinci
> >> drivers are using this to request channels - they need to support DT and
> >> legacy mode.
> > I think we should hide these things behind the API and do this behind the
> > hood for ACPI/DT systems.
> > 
> > Also it makes sense to use right API and mark rest as depricated
> 
> So to convert the dma_request_slave_channel_compat() and not to create _reason
> variant?
> 
> Or to have single API to request channel? The problem with that is that we
> need different parameters for legacy and DT for example.
Sorry this slipped thru

Thinking about it again, I think we should coverge to two APIs and mark the
legacy depracuated and look to convert folks and phase that out


-- 
~Vinod
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