lkml.org 
[lkml]   [2019]   [Jan]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [RFC PATCH] drm: disable WC optimization for cache coherent devices on non-x86
On Mon, 21 Jan 2019 at 16:07, Christoph Hellwig <hch@infradead.org> 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?

\
 
 \ /
  Last update: 2019-01-21 16:33    [W:0.086 / U:22.688 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site