[PATCH 11/31] dma: add channel request API that supports deferred probe

Dan Williams dan.j.williams at intel.com
Wed Nov 20 14:15:58 EST 2013

On Wed, Nov 20, 2013 at 10:24 AM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 11/19/2013 05:38 PM, Dan Williams wrote:
>> On Tue, Nov 19, 2013 at 4:09 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>> Deferred probe certainly isn't the only error that can be returned
>>> though,
>> Of course, but do any of those other ones matter?  Certainly not if
>> they've all been hidden behind a NULL return from
>> dma_request_slave_channel().
>>> so I don't think "defer" in the name makes much sense. The
>>> function as I wrote it returns a standard "error pointer" value.
>>> Typically, callers would simply propagate *any* error code back to the
>>> caller of probe() without even looking at it; it's the driver core that
>>> checks for -EPROBE_DEFER vs. other error codes. In some cases, drivers
>>> do check in order to avoid printing failure messages in the deferred
>>> probe case, but again that's pretty standard, and not something specific
>>> to this API.
>> Right, but the only reason to introduce this API is to propagate
>> EPROBE_DEFER, right?  It also serves to document drivers that are
>> prepared for / depend on deferred probing support.
> Well, that's the reason I'm introducing the API, but it's not really
> what the API actually does.

True, this is quite a bit of back and forth for something that will be
temporary.  How bad would it be to short-circuit this discussion and
go straight to converting dma_request_slave_channel().  Leave
dma_request_channel() as is and just convert the 20 or so users of
dma_request_slave_channel() over?

Also seems you could drop the changes to acpi-dma.c altogether if we
pass the result through IS_ERR_OR_NULL().

> That said, in the interests of moving this forward, I'll go for your
> suggested name dma_slave_request_channel_defer().
> Do I need an ack from Vinod on the function name, or the patches?

Yes, Vinod should ultimately ack all dma-slave patches... and throw in
another name recommendation for good measure ;-).

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