From: Arnd Bergmann <arnd@arndb.de>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Will Deacon <Will.Deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ding Tianhong <dingtianhong@huawei.com>
Subject: Re: For the problem when using swiotlb
Date: Fri, 21 Nov 2014 18:04:28 +0100 [thread overview]
Message-ID: <2530749.roRsteyaXx@wuerfel> (raw)
In-Reply-To: <20141121165708.GF19783@e104818-lin.cambridge.arm.com>
On Friday 21 November 2014 16:57:09 Catalin Marinas wrote:
> On Fri, Nov 21, 2014 at 12:48:09PM +0000, Arnd Bergmann wrote:
> > On Friday 21 November 2014 09:35:10 Catalin Marinas wrote:
> > > +static inline int dma_set_coherent_mask(struct device *dev, u64 mask)
> > > +{
> > > + if (!dma_supported(dev, mask))
> > > + return -EIO;
> > > + if (mask > dev->coherent_dma_mask)
> > > + mask &= of_dma_get_range_mask(dev);
> > > + dev->coherent_dma_mask = mask;
> > > + return 0;
> > > +}
> >
> > There is an interesting side problem here: the dma mask points to
> > coherent_dma_mask for all devices probed from DT, so this breaks
> > if we have any driver that sets them to different values. It is a
> > preexisting problem them.
>
> Such drivers would have to set both masks separately (or call
> dma_set_mask_and_coherent). What we assume though is that dma-ranges
> refers to both dma_mask and coherent_dma_mask. I don't think that would
> be a problem for ARM systems.
Right, I'm just saying that we don't have a way to detect drivers that
break this assumption, not that we have a serious problem already.
> > > EXPORT_SYMBOL_GPL(of_dma_get_range);
> > >
> > > +u64 of_dma_get_range_mask(struct device *dev)
> > > +{
> > > + u64 dma_addr, paddr, size;
> > > +
> > > + /* no dma mask limiting if no of_node or no dma-ranges property */
> > > + if (!dev->of_node ||
> > > + of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size) < 0)
> > > + return DMA_BIT_MASK(64);
> >
> > If no dma-ranges are present, we should assume that the bus only supports
> > 32-bit DMA, or we could make it architecture specific. It would probably
> > be best for arm64 to require a dma-ranges property for doing any DMA
> > at all, but we can't do that on arm32 any more now.
>
> I thought about this but it could break some existing arm64 DT files if
> we mandate dma-ranges property (we could try though). The mask limiting
> is arch-specific anyway.
Yes, this has taken far too long to get addressed, we should have added
the properties right from the start. If we have a function in architecture
specific code, maybe we can just check for the short list of already
supported platforms that need backwards compatibility and require the
mask for everything else?
> > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > > index 3b64d0bf5bba..50d1ac4739e6 100644
> > > --- a/drivers/of/platform.c
> > > +++ b/drivers/of/platform.c
> > > @@ -200,6 +200,10 @@ static void of_dma_configure(struct device *dev)
> > > /* DMA ranges found. Calculate and set dma_pfn_offset */
> > > dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
> > > dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
> > > +
> > > + /* limit the coherent_dma_mask to the dma-ranges size property */
> >
> > I would change the comment to clarify that we are actually changing
> > the dma_mask here as well.
> >
> > > + if (size < (1ULL << 32))
> > > + dev->coherent_dma_mask = DMA_BIT_MASK(ilog2(size));
> > > }
> >
> > As you mentioned in another mail in this thread, we wouldn't be
> > able to suuport this case on arm64.
>
> The mask would still be valid and even usable if an IOMMU is present. Do
> you mean we should not limit it at all here?
The code is certainly correct on arm32, as long as we have an appropriate
DMA zone.
> There is a scenario where smaller mask would work on arm64. For example
> Juno, you can have 2GB of RAM in the 32-bit phys range (starting at
> 0x80000000). A device with 31-bit mask and a dma_pfn_offset of
> 0x80000000 would still work (there isn't any but just as an example). So
> the check in dma_alloc_coherent() would be something like:
>
> phys_to_dma(top of ZONE_DMA) - dma_pfn_offset <= coherent_dma_mask
>
> (or assuming RAM starts at 0 and ignoring dma_pfn_offset for now)
>
> If the condition above fails, dma_alloc_coherent() would no longer fall
> back to swiotlb but issue a dev_warn() and return NULL.
Ah, that looks like it should work on all architectures, very nice.
How about checking this condition, and then printing a small warning
(dev_warn, not WARN_ON) and setting the dma_mask pointer to NULL?
Arnd
next prev parent reply other threads:[~2014-11-21 17:04 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-17 11:56 For the problem when using swiotlb Ding Tianhong
2014-11-17 12:18 ` Arnd Bergmann
2014-11-17 18:09 ` Catalin Marinas
2014-11-19 3:17 ` Ding Tianhong
2014-11-19 8:45 ` Arnd Bergmann
2014-11-19 11:29 ` Catalin Marinas
2014-11-19 12:48 ` Arnd Bergmann
2014-11-19 15:46 ` Catalin Marinas
2014-11-19 15:56 ` Arnd Bergmann
2014-11-21 11:06 ` Catalin Marinas
2014-11-21 11:26 ` Arnd Bergmann
2014-11-21 11:36 ` Catalin Marinas
2014-11-21 12:27 ` Arnd Bergmann
2014-11-20 2:57 ` Ding Tianhong
2014-11-20 7:40 ` Arnd Bergmann
2014-11-20 8:34 ` Ding Tianhong
2014-11-20 9:02 ` Arnd Bergmann
2014-11-20 9:21 ` Ding Tianhong
2014-11-21 9:35 ` Catalin Marinas
2014-11-21 10:32 ` Catalin Marinas
2014-11-21 12:48 ` Arnd Bergmann
2014-11-21 16:57 ` Catalin Marinas
2014-11-21 17:04 ` Arnd Bergmann [this message]
2014-11-21 17:51 ` Catalin Marinas
2014-11-21 18:09 ` Catalin Marinas
2014-11-24 20:12 ` Arnd Bergmann
2014-11-25 10:58 ` Catalin Marinas
2014-11-25 11:29 ` Russell King - ARM Linux
2014-11-25 12:23 ` Catalin Marinas
2014-11-27 2:36 ` Ding Tianhong
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2530749.roRsteyaXx@wuerfel \
--to=arnd@arndb.de \
--cc=Will.Deacon@arm.com \
--cc=catalin.marinas@arm.com \
--cc=dingtianhong@huawei.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).