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

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Date:	Tue, 2 Jun 2015 18:25:35 +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 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
> 
> But it is doable to do this for both the non _compat and _compat version:
> 1. change all users to check IS_ERR_OR_NULL(chan)
>  return the PTR_ERR if not NULL, or do whatever the driver was doing in case
> of chan == NULL.
> 2. change the non _compat and _compat versions to do the same as the _reason
> variants, #define the _reason ones to the non _reason names
> 3. Rename the _reason use to non _reason function in drivers
> 4. Remove the #defines for the _reason functions
> 5. Change the IS_ERR_OR_NULL(chan) to IS_ERR(chan) in all drivers
> The result:
> Both dma_request_slave_channel() and dma_request_slave_channel_compat() will
> return ERR_PTR in case of failure or in success they will return the pinter to
> chan.
> 
> Is this what you were asking?
> It is a bit broader than what this series was doing: taking care of
> OMAP/daVinci drivers for deferred probing regarding to dmaengine ;)
Yes but it would make sense right? I know it is a larger work but then we
wouldn't want another dma_request_slave_xxx API, at some point we have stop
it exapnding, perhpas now :)

Yes I am all ears to stage this work and not do transition gardually..

-- 
~Vinod
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