lkml.org 
[lkml]   [2020]   [Apr]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3 02/16] mfd: mfd-core: Don't overwrite the dma_mask of the child device
From
Date
On 2020-04-28 1:45 pm, Andy Shevchenko wrote:
> On Thu, Apr 23, 2020 at 07:45:29PM +0200, Michael Walle wrote:
>> Commit cdfee5623290 ("driver core: initialize a default DMA mask for
>> platform device") initialize the DMA of a platform device. But if the
>> parent doesn't have a dma_mask set, for example if it's an I2C device,
>> the dma_mask of the child platform device will be set to zero again.
>> Which leads to many "DMA mask not set" warnings, if the MFD cell has the
>> of_compatible property set.
>
> I'm wondering why parent doesn't have it.

Because the parent isn't on a DMA-capable bus, and thus really shouldn't
have a valid DMA configuration ever.

> I remember we have explicit patches in the past for buses such as PCI and AMBA
> to set default DMA mask for all physical devices on the respective bus, of
> course they can individually override it later.
>
> So, this seems to me a paper over the real issue (absence of default DMA mask
> where it's needed) and devices should explicitly define it if they disagree
> with default.
>
> If I'm wrong, you really need elaborate commit message much better.

The problem here is that MFD children are created as platform devices
(regardless of what their parent is) and assigned an of_node, at which
point they look pretty much indistinguishable from SoC devices created
by the of_platform code, that *do* have to be assumed to be DMA-capable
to prevent ~90% of existing devicetrees from breaking.

Of course the real fundamental issue is the platform bus itself, but
it's way too late to fix that :(

Robin.

\
 
 \ /
  Last update: 2020-04-28 15:07    [W:0.101 / U:0.620 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site