From: Peter Ujfalusi <peter.ujfalusi@ti.com>
To: Christoph Hellwig <hch@lst.de>
Cc: robh@kernel.org, vigneshr@ti.com, konrad.wilk@oracle.com,
linux@armlinux.org.uk, linux-kernel@vger.kernel.org,
iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel@lists.infradead.org, rogerq@ti.com
Subject: Re: [PoC] arm: dma-mapping: direct: Apply dma_pfn_offset only when it is valid
Date: Fri, 31 Jan 2020 16:00:03 +0200 [thread overview]
Message-ID: <54af6531-705f-a31c-c5b8-479261a5454e@ti.com> (raw)
In-Reply-To: <20200130164010.GA6472@lst.de>
Hi Christoph,
On 30/01/2020 18.40, Christoph Hellwig wrote:
> On Thu, Jan 30, 2020 at 03:04:37PM +0200, Peter Ujfalusi via iommu wrote:
>> On 30/01/2020 9.53, Christoph Hellwig wrote:
>>> [skipping the DT bits, as I'm everything but an expert on that..]
>>>
>>> On Mon, Jan 27, 2020 at 04:00:30PM +0200, Peter Ujfalusi wrote:
>>>> I agree on the phys_to_dma(). It should fail for addresses which does
>>>> not fall into any of the ranges.
>>>> It is just a that we in Linux don't have the concept atm for ranges, we
>>>> have only _one_ range which applies to every memory address.
>>>
>>> what does atm here mean?
>>
>> struct device have only single dma_pfn_offset, one can not have multiple
>> ranges defined. If we have then only the first is taken and the physical
>> address and dma address is discarded, only the dma_pfn_offset is stored
>> and used.
>>
>>> We have needed multi-range support for quite a while, as common broadcom
>>> SOCs do need it. So patches for that are welcome at least from the
>>> DMA layer perspective (kinda similar to your pseudo code earlier)
>>
>> But do they have dma_pfn_offset != 0?
>
> Well, with that I mean multiple ranges with different offsets. Take
> a look at arch/mips/bmips/dma.c:__phys_to_dma() and friends. This
> is an existing implementation for mips, but there are arm and arm64
> SOCs using the same logic on the market as well, and we'll want to
> support them eventually.
I see. My PoC patch was not too off then ;)
So the plan is to have a generic implementation for all of the
architecture, right?
>> The dma_pfn_offset is _still_ applied to the mask we are trying to set
>> (and validate) via dma-direct.
>
> And for the general case that is exactly the right thing to do, we
> just need to deal with really odd ZONE_DMA placements like yours.
I'm still not convinced, the point of the DMA mask, at least how I see
it, to check that the dma address can be handled by the device (DMA,
peripheral with built in DMA, etc), it is not against physical address.
Doing phys_to_dma() on the mask from the dma_set_mask() is just wrong.
>>> We'll need to find the minimum change to make it work
>>> for now without switching ops, even if it isn't the correct one, and
>>> then work from there.
>>
>> Sure, but can we fix the regression by reverting to arm_ops for now only
>> if dma_pfn_offset is not 0? It used to work fine in the past at least it
>> appeared to work on K2 platforms.
>
> But that will cause yet another regression in what we have just fixed
> with using the generic direct ops, at which points it turns into who
> screams louder.
Hehe, I see.
I genuinely curious why k2 platform worked just fine with LPAE (it needs
it), but guys had issues with LPAE on dra7/am5.
The fix for dra7/am5 broke k2.
As far as I can see the main (only) difference is that k2 have
dma_pfn_offset = 0x780000, while dra7/am5 have it 0 (really direct mapping).
> For now I'm tempted to throw something like this in, which is a bit
> of a hack, but actually 100% matches what various architectures have
> historically done:
>
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 6af7ae83c4ad..6ba9ee6e20bd 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -482,6 +482,9 @@ int dma_direct_supported(struct device *dev, u64 mask)
> {
> u64 min_mask;
>
> + if (mask >= DMA_BIT_MASK(32))
> + return 1;
> +
Right, so skipping phys_to_dma() for the mask and believing that it will
work..
It does: audio and dmatest memcpy tests are just fine with this, MMC
also probed with ADMA enabled.
As far as I can tell it works as well as falling back to the old arm ops
in case of LPAE && dma_pfn_offset != 0
Fwiw:
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Would you be comfortable to send apply this patch to mainline with
Fixes: ad3c7b18c5b3 ("arm: use swiotlb for bounce buffering on LPAE
configs")
So it gets picked for stable kernels as well?
> if (IS_ENABLED(CONFIG_ZONE_DMA))
> min_mask = DMA_BIT_MASK(zone_dma_bits);
> else
>
Thank you,
- Péter
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
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next prev parent reply other threads:[~2020-01-31 13:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-09 14:20 add swiotlb support to arm32 Christoph Hellwig
2019-07-09 14:20 ` [PATCH 1/2] dma-mapping check pfn validity in dma_common_{mmap, get_sgtable} Christoph Hellwig
2019-07-09 14:20 ` [PATCH 2/2] arm: use swiotlb for bounce buffer on LPAE configs Christoph Hellwig
2019-07-24 17:23 ` Nicolas Saenz Julienne
2019-07-24 17:55 ` Christoph Hellwig
2019-12-19 13:10 ` Peter Ujfalusi
2019-12-19 15:02 ` Christoph Hellwig
2019-12-19 15:20 ` Peter Ujfalusi
2020-01-08 8:28 ` Peter Ujfalusi
2020-01-08 12:21 ` Robin Murphy
2020-01-08 14:00 ` Peter Ujfalusi
2020-01-08 15:20 ` Robin Murphy
2020-01-09 14:49 ` Christoph Hellwig
2020-01-14 10:43 ` Peter Ujfalusi
2020-01-14 16:43 ` [PoC] arm: dma-mapping: direct: Apply dma_pfn_offset only when it is valid Peter Ujfalusi
2020-01-14 18:19 ` Robin Murphy
2020-01-15 11:50 ` Peter Ujfalusi
2020-01-16 19:13 ` Robin Murphy
2020-01-27 14:00 ` Peter Ujfalusi
2020-01-30 7:53 ` Christoph Hellwig
2020-01-30 13:04 ` Peter Ujfalusi
2020-01-30 16:40 ` Christoph Hellwig
2020-01-31 13:59 ` Peter Ujfalusi
2020-01-31 14:00 ` Peter Ujfalusi [this message]
2020-01-31 14:00 ` Peter Ujfalusi
2020-02-03 17:08 ` Christoph Hellwig
2020-02-05 10:19 ` Peter Ujfalusi
2019-07-17 13:21 ` add swiotlb support to arm32 Vignesh Raghavendra
2019-07-19 12:33 ` Christoph Hellwig
2019-07-24 15:37 ` Christoph Hellwig
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