[PATCH] mfd: mfd-core: Don't overwrite the dma_mask of the child device

[PATCH] mfd: mfd-core: Don't overwrite the dma_mask of the child device

[Michael Walle]

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.

[    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 don't overwrite the dma_mask of the children. Instead set the
dma_mask of the platform device.

Signed-off-by: Michael Walle <michael@walle.cc>
Suggested-by: Robin Murphy <robin.murphy@arm.com>
---
Former discussion was here:
https://lore.kernel.org/lkml/20200423174543.17161-3-michael@walle.cc/

Because my MFD driver now uses of_platform_populate() it doesn't trigger
this anymore. But it may be useful for others, e.g. if I'm not mistaken it
should apply to the mt6360 sub devices.

Thus I'm submitting this patch seperately.

 drivers/mfd/mfd-core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
index f5a73af60dd4..e735565969b3 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->platform_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;
 
-- 
2.20.1

Re: [PATCH] mfd: mfd-core: Don't overwrite the dma_mask of the child device

[Andy Shevchenko]

On Thu, Jun 04, 2020 at 11:30:37PM +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.
> 
> [    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 don't overwrite the dma_mask of the children. Instead set the
> dma_mask of the platform device.

> ---
> Former discussion was here:
> https://lore.kernel.org/lkml/20200423174543.17161-3-michael@walle.cc/
> 
> Because my MFD driver now uses of_platform_populate() it doesn't trigger
> this anymore. But it may be useful for others, e.g. if I'm not mistaken it
> should apply to the mt6360 sub devices.

Yeah, I'm not sure it's right thing to do, but let maintainers and more
experienced in topic developers to speak up.

-- 
With Best Regards,
Andy Shevchenko