From: Christoph Hellwig <hch@lst.de>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christoph Hellwig <hch@lst.de>,
iommu@lists.linux-foundation.org,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size
Date: Thu, 27 Sep 2018 15:49:54 +0200 [thread overview]
Message-ID: <20180927134954.GB8281@lst.de> (raw)
In-Reply-To: <985079efc3296ac45de1e6344d7916c42fc7cbdd.camel@kernel.crashing.org>
On Thu, Sep 27, 2018 at 11:50:14AM +1000, Benjamin Herrenschmidt wrote:
> > - * to be able to satisfy them - either by not supporting more physical
> > - * memory, or by providing a ZONE_DMA32. If neither is the case, the
> > - * architecture needs to use an IOMMU instead of the direct mapping.
> > - */
> > - if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
> > + u64 min_mask;
> > +
> > + if (IS_ENABLED(CONFIG_ZONE_DMA))
> > + min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
> > + else
> > + min_mask = min_t(u64, DMA_BIT_MASK(32),
> > + (max_pfn - 1) << PAGE_SHIFT);
> > +
> > + if (mask >= phys_to_dma(dev, min_mask))
> > return 0;
>
> nitpick ... to be completely "correct", I would have written
>
> if (IS_ENABLED(CONFIG_ZONE_DMA))
> min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
> else
> min_mask = DMA_BIT_MASK(32);
>
> min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
>
> In "theory" it's also ok to have a mask < ZONE_DMA_BITS as long as it's
> big enough to fit all memory :-)
Yeah, we could do that.
next prev parent reply other threads:[~2018-09-27 13:49 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-20 18:52 dma mask related fixups (including full bus_dma_mask support) Christoph Hellwig
2018-09-20 18:52 ` [PATCH 1/5] dma-mapping: make the get_required_mask method available unconditionally Christoph Hellwig
2018-09-27 1:28 ` Benjamin Herrenschmidt
2018-09-20 18:52 ` [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask Christoph Hellwig
2018-09-27 1:31 ` Benjamin Herrenschmidt
2018-09-27 14:12 ` Robin Murphy
2018-09-27 15:28 ` Christoph Hellwig
2018-09-27 15:35 ` Robin Murphy
2018-09-20 18:52 ` [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection Christoph Hellwig
2018-09-27 1:45 ` Benjamin Herrenschmidt
2018-09-27 13:49 ` Christoph Hellwig
2018-09-28 0:06 ` Benjamin Herrenschmidt
2018-09-28 15:46 ` Christoph Hellwig
2018-09-27 14:30 ` Robin Murphy
2018-09-27 15:30 ` Christoph Hellwig
2018-09-27 15:38 ` Robin Murphy
2018-09-27 15:41 ` Christoph Hellwig
2018-09-20 18:52 ` [PATCH 4/5] dma-direct: implement complete bus_dma_mask handling Christoph Hellwig
2018-09-27 14:58 ` Robin Murphy
2018-09-27 15:32 ` Christoph Hellwig
2018-09-27 16:14 ` Robin Murphy
2018-09-27 16:27 ` Christoph Hellwig
2018-09-27 16:41 ` Robin Murphy
2018-09-20 18:52 ` [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size Christoph Hellwig
2018-09-27 1:50 ` Benjamin Herrenschmidt
2018-09-27 13:49 ` Christoph Hellwig [this message]
2018-09-27 15:07 ` Robin Murphy
2018-09-27 22:35 dma mask related fixups (including full bus_dma_mask support) v2 Christoph Hellwig
2018-09-27 22:35 ` [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size Christoph Hellwig
2018-10-03 23:10 ` Alexander Duyck
2018-10-09 5:01 ` Benjamin Herrenschmidt
2018-11-19 14:18 ` Ramon Fried
2018-11-19 15:50 ` Robin Murphy
2018-11-20 7:38 ` Ramon Fried
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