lkml.org 
[lkml]   [2014]   [May]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/5] dma-mapping: Add devm_ interface for dma_map_single()
Hello Tejun,

On 17/05/14 00:08, Tejun Heo wrote:
>
> Don't we wanna map the underlying operation - dma_map_single_attrs() -
> instead?
>

I'll resubmit this patch promptly, with a follow-up patch for the diff
to implement dmam_map_single_attrs() instead. Plus a define-statement
for dmam_map_single(). I can't test the case of a non-NULL value for
@attrs however.

>
>> + if (dma_mapping_error(dev, dma_handle)) {
>> + devres_free(dr);
>> + return 0;
>>
> Can't we just keep returning dma_handle? Even if that means invoking
> ->mapping_error() twice? It's yucky to have subtly different error
> return especially because in most cases it won't fail.
>
Yucky it is indeed. There are however two problems with keeping the
existing API:

* What to do if devres_alloc() fails. How do I signal back an error? The
only way I can think of is returning zero. But if the caller should know
that zero means failure, I've already broken the API. I might as well
return zero for any kind of failure.
* It seems like a lot of dma_mapping_error() implementations always
return no-error, since the DMA mapping can't fail on specific
architectures. If callers use dma_mapping_error(), the possible
devres_alloc() failure will be missed.

By the way, where I've seen dma_mapping_error() doing something, it
checks for dma_handle == 0.

Submitting updated patches for the DMA mapping part soon.

Regards,
Eli




\
 
 \ /
  Last update: 2014-05-17 15:01    [W:0.084 / U:1.224 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site