Re: [PATCH v7 05/10] mfd: sec: set DMA coherent mask

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Shared dma_mask pointer across MFD child devices causes a data race and violates DMA API contracts.
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commit cc615ed9ba9013f030c19361a7a4d79aad2e467d
Author: Kaustabh Chakraborty <kauschluss@disroot.org>

mfd: sec: set DMA coherent mask

This commit manually sets the coherent DMA mask to 0 and points the device's
dma_mask to it. This is intended to suppress "DMA mask not set" warnings
for sub-devices, as the device does not use DMA for communication.

> diff --git a/drivers/mfd/sec-common.c b/drivers/mfd/sec-common.c
> index 22f6c74eb6c0e..fe92bc4a3dd26 100644
> --- a/drivers/mfd/sec-common.c
> +++ b/drivers/mfd/sec-common.c
> @@ -221,6 +221,9 @@ int sec_pmic_probe(struct device *dev, int device_type, unsigned int irq,
>  	if (IS_ERR(irq_data))
>  		return PTR_ERR(irq_data);
>  
> +	dev->coherent_dma_mask = 0;
> +	dev->dma_mask = &dev->coherent_dma_mask;

When the MFD core adds child devices via mfd_add_device(), it copies the
parent's dma_mask pointer to the child devices:

    pdev->dev.dma_mask = parent->dma_mask;

Because sub-devices for this PMIC probe asynchronously, they can concurrently
execute platform_dma_configure(), which eventually calls of_dma_configure_id()
and performs a lockless read-modify-write:

    *dev->dma_mask &= mask;

Since all child devices share the same dma_mask pointer referencing the
parent's coherent_dma_mask, does this cause an unsynchronized data race on
the parent's memory?

Additionally, sharing a single dma_mask pointer across multiple devices breaks
the driver model. If any child device were to legitimately call dma_set_mask(),
wouldn't it silently overwrite the DMA mask for all sibling devices?

Finally, manually modifying device structures to fake an invalid mask of 0
bypasses DMA subsystem validation. Helpers like dma_coerce_mask_and_coherent()
explicitly reject a mask of 0. Is manually assigning 0 here the recommended way
to suppress the warning?

> +
>  	pm_runtime_set_active(sec_pmic->dev);
>  
>  	switch (sec_pmic->device_type) {

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Sashiko AI review · https://sashiko.dev/#/patchset/20260516-s2mu005-pmic-v7-0-73f9702fb461@disroot.org?part=5