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

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Message-ID: <55687892.7050606@ti.com>
Date:	Fri, 29 May 2015 17:32:50 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Vinod Koul <vinod.koul@...el.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	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 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.

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 ;)

-- 
Péter
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