On Mon, 21 Jan 2019 at 16:07, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> > +#include <linux/dma-noncoherent.h>
>
> This header is not for usage in device drivers, but purely for
> dma-mapping implementations!
>
Is that documented anywhere?
> > +static inline bool drm_device_can_wc_memory(struct drm_device *ddev)
> > {
> > + if (IS_ENABLED(CONFIG_PPC))
> > + return IS_ENABLED(CONFIG_NOT_COHERENT_CACHE);
> > + else if (IS_ENABLED(CONFIG_MIPS))
> > + return !IS_ENABLED(CONFIG_CPU_LOONGSON3);
> > + else if (IS_ENABLED(CONFIG_X86))
> > + return true;
> > +
> > + return !dev_is_dma_coherent(ddev->dev);
>
> And even if something like this was valid to do, it would have to be
> a core function with an arch hook, and not hidden in a random driver.
Why would it not be valid to do? Is it wrong for a driver to be aware
of whether a device is cache coherent or not?
And in case it isn't, do you have an alternative suggestion on how to
fix this mess?
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