[OpenRISC] [PATCH 1/2] dma-mapping: zero memory returned from dma_alloc_*

Geert Uytterhoeven
2018-12-14T12:36:26Z

Hi Christoph,

On Fri, Dec 14, 2018 at 12:47 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Fri, Dec 14, 2018 at 10:54:32AM +0100, Geert Uytterhoeven wrote:
> > > - page = alloc_pages(flag, order);
> > > + page = alloc_pages(flag | GFP_ZERO, order);
> > > if (!page)
> > > return NULL;
> >
> > There's second implementation below, which calls __get_free_pages() and
> > does an explicit memset(). As __get_free_pages() calls alloc_pages(), perhaps
> > it makes sense to replace the memset() by GFP_ZERO, to increase consistency?
>
> It would, but this patch really tries to be minimally invasive to just
> provide the zeroing everywhere.

Fair enough.

> There is plenty of opportunity
> to improve the m68k dma allocator if I can get enough reviewers/testers:
>
> - for one the coldfire/nommu case absolutely does not make sense to
> me as there is not work done at all to make sure the memory is
> mapped uncached despite the architecture implementing cache
> flushing for the map interface. So this whole implementation
> looks broken to me and will need some major work (I had a previous
> discussion with Greg on that which needs to be dug out)
> - the "regular" implementation in this patch should probably be replaced
> with the generic remapping helpers that have been added for the 4.21
> merge window:
>
> http://git.infradead.org/users/hch/dma-mapping.git/commitdiff/0c3b3171ceccb8830c2bb5adff1b4e9b204c1450
>
> Compile tested only patch below:
>
> --
> From ade86dc75b9850daf9111ebf9ce15825a6144f2d Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Fri, 14 Dec 2018 12:41:45 +0100
> Subject: m68k: use the generic dma coherent remap allocator
>
> This switche to using common code for the DMA allocations, including
> potential use of the CMA allocator if configure. Also add a few
> comments where the existing behavior seems to be lacking.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Thanks, looks OK to me.
M68k doesn't have many drivers using the DMA framework, as most of them
predated that framework.

> --- a/arch/m68k/kernel/dma.c
> +++ b/arch/m68k/kernel/dma.c

>
> -void arch_dma_free(struct device *dev, size_t size, void *addr,
> - dma_addr_t handle, unsigned long attrs)
> +pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
> + unsigned long attrs)
> {
> - pr_debug("dma_free_coherent: %p, %x\n", addr, handle);
> - vfree(addr);
> + /*
> + * XXX: this doesn't seem to handle the sun3 MMU at all.

Sun-3 selects NO_DMA, and this file is compiled for the HAS_DMA case only.

> + */
> + if (CPU_IS_040_OR_060) {
> + pgprot_val(prot) &= ~_PAGE_CACHE040;
> + pgprot_val(prot) |= _PAGE_GLOBAL040 | _PAGE_NOCACHE_S;
> + } else {
> + pgprot_val(prot) |= _PAGE_NOCACHE030;
> + }
> + return prot;
> }

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds