Re: Onboard SD card doesn't work anymore after the 'mmc-v5.4-2' updates

[Rob Herring <robh+dt@kernel.org>]

On Wed, Oct 23, 2019 at 1:41 AM Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
>
> On Wed, 2019-10-23 at 16:42 +1100, Michael Ellerman wrote:
> >
> > Right, it seems of_dma_is_coherent() has baked in the assumption that
> > devices are non-coherent unless explicitly marked as coherent.
> >
> > Which is wrong on all or at least most existing powerpc systems
> > according to Ben.
>
> This is probably broken on sparc(64) as well and whatever else uses
> DT and is an intrinsicly coherent architecture (did we ever have
> DT enabled x86s ? Wasn't OLPC such a beast ?).

Only if those platforms use one of the 5 drivers that call this function:

drivers/ata/ahci_qoriq.c:       qoriq_priv->is_dmacoherent =
of_dma_is_coherent(np);
drivers/crypto/ccree/cc_driver.c:       new_drvdata->coherent =
of_dma_is_coherent(np);
drivers/iommu/arm-smmu-v3.c:    if (of_dma_is_coherent(dev->of_node))
drivers/iommu/arm-smmu.c:       if (of_dma_is_coherent(dev->of_node))
drivers/mmc/host/sdhci-of-esdhc.c:      if (of_dma_is_coherent(dev->of_node))

Curious that a PPC specific driver (ahci_qoriq) calls it...

Note that the value is also passed to arch_setup_dma_ops(), but only
arc, arm, arm64, and mips implement arch_setup_dma_ops.

> I think this should have been done the other way around and default to
> coherent since most traditional OF platforms are coherent, and you
> can't just require those DTs to change.

You can blame me. This was really only intended for cases where
coherency is configurable on a per peripheral basis and can't be
determined in other ways.

The simple solution here is simply to use the compatible string for
the device to determine coherent or not.

Rob