Messages in this thread | | | Subject | Re: [PATCH v3 02/16] mfd: mfd-core: Don't overwrite the dma_mask of the child device | From | Robin Murphy <> | Date | Tue, 28 Apr 2020 14:06:20 +0100 |
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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.
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