Messages in this thread | | | Date | Wed, 11 Mar 2020 14:10:04 +0100 | From | Michael Walle <> | Subject | Re: [RFC PATCH] mfd: mfd-core: inherit only valid dma_masks/flags from parent |
| |
Am 2020-03-11 12:25, schrieb Robin Murphy: > 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.
Thanks for the explanation.
> 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;
That works.
-michael
> pdev->dev.dma_parms = parent->dma_parms; > pdev->dev.coherent_dma_mask = parent->coherent_dma_mask;
| |