Re: [RFC PATCH] mfd: mfd-core: inherit only valid dma_masks/flags from parent

[Michael Walle]

Am 2020-03-11 07:18, schrieb Christoph Hellwig:
> On Wed, Mar 11, 2020 at 12:09:35AM +0100, 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@xxxxxx>
> > Cc: Rob Herring <robh@xxxxxxxxxx>
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>
> > Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> > Signed-off-by: Michael Walle <michael@xxxxxxxx>
> > ---
> >
> > 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.
> >
> > There was also a thread [1] about this topic, but there seems to be no
> > conclusion.
> >
> > [1] https://www.spinics.net/lists/linux-renesas-soc/msg31581.html
> >
> >  drivers/mfd/mfd-core.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> > index b9eb8f40c073..5d8ea5e8e93c 100644
> > --- a/drivers/mfd/mfd-core.c
> > +++ b/drivers/mfd/mfd-core.c
> > @@ -139,9 +139,12 @@ 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->dev.dma_parms = parent->dma_parms;
> > -	pdev->dev.coherent_dma_mask = parent->coherent_dma_mask;
> > +	if (parent->dma_mask)
> > +		pdev->dev.dma_mask = parent->dma_mask;
> > +	if (parent->dma_parms)
> > +		pdev->dev.dma_parms = parent->dma_parms;
>
> Both of these are pointers, and we can't just share them.  You need
> to allocate storage for them and the allocate the values over.

So they were alreay copied wrong before this patch? If so, should
there be a fixes patch for it? The commit who introduced the copy
dates back to 2013:
  b018e1361bad3 mfd: core: Copy DMA mask and params from parent

-michael