Messages in this thread Patch in this message | | | Subject | Re: [RFC PATCH] mfd: mfd-core: inherit only valid dma_masks/flags from parent | From | Robin Murphy <> | Date | Wed, 11 Mar 2020 11:25:05 +0000 |
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On 2020-03-10 11:09 pm, Michael Walle wrote: > Only copy the dma_masks and flags from the parent device, if the parent > has a valid dma_mask/flags. Commit cdfee5623290 ("driver core: > initialize a default DMA mask for platform device") initialize the DMA > masks 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. > > [ 1.877937] sl28cpld-pwm sl28cpld-pwm: DMA mask not set > [ 1.883282] sl28cpld-pwm sl28cpld-pwm.0: DMA mask not set > [ 1.888795] sl28cpld-gpio sl28cpld-gpio: DMA mask not set > > Thus a MFD child should just inherit valid dma_masks and keep the > platform default otherwise. > > Cc: Christoph Hellwig <hch@lst.de> > Cc: Rob Herring <robh@kernel.org> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: Russell King <linux@armlinux.org.uk> > Signed-off-by: Michael Walle <michael@walle.cc> > --- > > Hi, > > I don't know if that is the correct way of handling things. Maybe I'm > also doing something wrong in my driver, I had a look at other I2C MFD > drivers but couldn't find a clue why they shouldn't have the same > problem.
The underlying issue is that about 99% of MFD children should not be going through dma_configure() at all because their parent 'real' device is not on a DMA-capable bus, but as they are platform devices we are forced to give them the benefit of the doubt. For DT systems the only vaguely-reasonable heuristic to distinguish between "platform" meaning "SoC memory-mapped device" and "platform" meaning "random crap made up by Linux" is whether the device has a populated OF node, but MFD's trick of hanging the parent device's OF node onto its synthesised children kicks a hole right through even that.
Modulo any other concerns with the existing code, does the change below make things work the way you want? It's still a bit of a bodge, but short of invasive large-scale changes with bus types I don't see a way to do the 'right' thing :/
Robin.
----->8----- diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c index f5a73af60dd4..1e4a6e8bd630 100644 --- a/drivers/mfd/mfd-core.c +++ b/drivers/mfd/mfd-core.c @@ -138,7 +138,7 @@ static int mfd_add_device(struct device *parent, int id,
pdev->dev.parent = parent; pdev->dev.type = &mfd_dev_type; - pdev->dev.dma_mask = parent->dma_mask; + pdev->dma_mask = parent->dma_mask ? *parent->dma_mask : 0; pdev->dev.dma_parms = parent->dma_parms; pdev->dev.coherent_dma_mask = parent->coherent_dma_mask;
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