| Message ID | 1505811161-25246-1-git-send-email-chenhc@lemote.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
On 19/09/17 09:52, Huacai Chen wrote: > We will use device_is_coherent() as a helper function, which will be > used in the next patch. > > There is a MIPS-specific plat_device_is_coherent(), but we need a more > generic solution, so add and use a new function pointer in dma_map_ops. I think we're heading in the right direction with the series, but I still don't like this patch. I can pretty much guarantee that driver authors *will* abuse a generic device_is_coherent() API to mean "I can skip other DMA API calls and just use virt_to_phys()". I think it would be far better to allow architectures to provide their own override of dma_get_cache_alignment(), and let the coherency detail remain internal to the relevant arch implementations. [...] > @@ -697,6 +698,15 @@ static inline void *dma_zalloc_coherent(struct device *dev, size_t size, > } > > #ifdef CONFIG_HAS_DMA > +static inline int device_is_coherent(struct device *dev) > +{ > + const struct dma_map_ops *ops = get_dma_ops(dev); > + if (ops && ops->device_is_coherent) > + return ops->device_is_coherent(dev); > + else > + return 1; /* compatible behavior */ That is also quite scary - if someone now adds a new dma_get_cache_alignemnt() call and dutifully passes a non-NULL device, they will now get back an alignment of 1 on all non-coherent platforms except MIPS: hello data corruption. Robin. > +} > + > static inline int dma_get_cache_alignment(void) > { > #ifdef ARCH_DMA_MINALIGN >
Hi, Robin,
Before 2.6.36 dma_get_cache_alignment is arch-dependent, and it is unified in commit 4565f0170dfc849b3629c27d7 ("dma-mapping: unify dma_get_cache_alignment implementations"). Should we revert to the old implementation?
Huacai
------------------ Original ------------------
From: "Robin Murphy"<robin.murphy@arm.com>;
Date: Thu, Sep 21, 2017 06:47 PM
To: "Huacai Chen"<chenhc@lemote.com>; "Christoph Hellwig"<hch@lst.de>;
Cc: "Marek Szyprowski"<m.szyprowski@samsung.com>; "Andrew Morton"<akpm@linux-foundation.org>; "Fuxin Zhang"<zhangfx@lemote.com>; "linux-kernel"<linux-kernel@vger.kernel.org>; "James E . J . Bottomley"<jejb@linux.vnet.ibm.com>; "Martin K . Petersen"<martin.petersen@oracle.com>; "linux-scsi"<linux-scsi@vger.kernel.org>; "stable"<stable@vger.kernel.org>;
Subject: Re: [PATCH V6 1/3] dma-mapping: Introduce device_is_coherent() as ahelper
On 19/09/17 09:52, Huacai Chen wrote:
> We will use device_is_coherent() as a helper function, which will be
> used in the next patch.
>
> There is a MIPS-specific plat_device_is_coherent(), but we need a more
> generic solution, so add and use a new function pointer in dma_map_ops.
I think we're heading in the right direction with the series, but I
still don't like this patch. I can pretty much guarantee that driver
authors *will* abuse a generic device_is_coherent() API to mean "I can
skip other DMA API calls and just use virt_to_phys()".
I think it would be far better to allow architectures to provide their
own override of dma_get_cache_alignment(), and let the coherency detail
remain internal to the relevant arch implementations.
[...]
> @@ -697,6 +698,15 @@ static inline void *dma_zalloc_coherent(struct device *dev, size_t size,
> }
>
> #ifdef CONFIG_HAS_DMA
> +static inline int device_is_coherent(struct device *dev)
> +{
> + const struct dma_map_ops *ops = get_dma_ops(dev);
> + if (ops && ops->device_is_coherent)
> + return ops->device_is_coherent(dev);
> + else
> + return 1; /* compatible behavior */
That is also quite scary - if someone now adds a new
dma_get_cache_alignemnt() call and dutifully passes a non-NULL device,
they will now get back an alignment of 1 on all non-coherent platforms
except MIPS: hello data corruption.
Robin.
> +}
> +
> static inline int dma_get_cache_alignment(void)
> {
> #ifdef ARCH_DMA_MINALIGN
>
On 22/09/17 03:13, 陈华才 wrote: > Hi, Robin, > > Before 2.6.36 dma_get_cache_alignment is arch-dependent, and it is unified in commit 4565f0170dfc849b3629c27d7 ("dma-mapping: unify dma_get_cache_alignment implementations"). Should we revert to the old implementation? Not quite - I mean instead of adding an ops->device_is_coherent callback (which cannot really have a safe fallback value either way) and trying to enforce that dma_get_cache_alignment() should be the only valid caller, just add an ops->get_cache_alignment callback directly. Robin. > > Huacai > > ------------------ Original ------------------ > From: "Robin Murphy"<robin.murphy@arm.com>; > Date: Thu, Sep 21, 2017 06:47 PM > To: "Huacai Chen"<chenhc@lemote.com>; "Christoph Hellwig"<hch@lst.de>; > Cc: "Marek Szyprowski"<m.szyprowski@samsung.com>; "Andrew Morton"<akpm@linux-foundation.org>; "Fuxin Zhang"<zhangfx@lemote.com>; "linux-kernel"<linux-kernel@vger.kernel.org>; "James E . J . Bottomley"<jejb@linux.vnet.ibm.com>; "Martin K . Petersen"<martin.petersen@oracle.com>; "linux-scsi"<linux-scsi@vger.kernel.org>; "stable"<stable@vger.kernel.org>; > Subject: Re: [PATCH V6 1/3] dma-mapping: Introduce device_is_coherent() as ahelper > > > On 19/09/17 09:52, Huacai Chen wrote: >> We will use device_is_coherent() as a helper function, which will be >> used in the next patch. >> >> There is a MIPS-specific plat_device_is_coherent(), but we need a more >> generic solution, so add and use a new function pointer in dma_map_ops. > > I think we're heading in the right direction with the series, but I > still don't like this patch. I can pretty much guarantee that driver > authors *will* abuse a generic device_is_coherent() API to mean "I can > skip other DMA API calls and just use virt_to_phys()". > > I think it would be far better to allow architectures to provide their > own override of dma_get_cache_alignment(), and let the coherency detail > remain internal to the relevant arch implementations. > > [...] >> @@ -697,6 +698,15 @@ static inline void *dma_zalloc_coherent(struct device *dev, size_t size, >> } >> >> #ifdef CONFIG_HAS_DMA >> +static inline int device_is_coherent(struct device *dev) >> +{ >> + const struct dma_map_ops *ops = get_dma_ops(dev); >> + if (ops && ops->device_is_coherent) >> + return ops->device_is_coherent(dev); >> + else >> + return 1; /* compatible behavior */ > > That is also quite scary - if someone now adds a new > dma_get_cache_alignemnt() call and dutifully passes a non-NULL device, > they will now get back an alignment of 1 on all non-coherent platforms > except MIPS: hello data corruption. > > Robin. > >> +} >> + >> static inline int dma_get_cache_alignment(void) >> { >> #ifdef ARCH_DMA_MINALIGN >> >
On Fri, Sep 22, 2017 at 02:44:51PM +0100, Robin Murphy wrote: > Not quite - I mean instead of adding an ops->device_is_coherent callback > (which cannot really have a safe fallback value either way) and trying > to enforce that dma_get_cache_alignment() should be the only valid > caller, just add an ops->get_cache_alignment callback directly. Exactly - and then fall back to ARCH_DMA_MINALIGN/1 if the ops vector is not provided, to keep the existing behavior.
diff --git a/arch/mips/cavium-octeon/dma-octeon.c b/arch/mips/cavium-octeon/dma-octeon.c index c64bd87..cd1a133 100644 --- a/arch/mips/cavium-octeon/dma-octeon.c +++ b/arch/mips/cavium-octeon/dma-octeon.c @@ -324,7 +324,8 @@ static struct octeon_dma_map_ops _octeon_pci_dma_map_ops = { .sync_sg_for_cpu = swiotlb_sync_sg_for_cpu, .sync_sg_for_device = octeon_dma_sync_sg_for_device, .mapping_error = swiotlb_dma_mapping_error, - .dma_supported = swiotlb_dma_supported + .dma_supported = swiotlb_dma_supported, + .device_is_coherent = plat_device_is_coherent }, }; diff --git a/arch/mips/loongson64/common/dma-swiotlb.c b/arch/mips/loongson64/common/dma-swiotlb.c index 34486c1..c758d9b 100644 --- a/arch/mips/loongson64/common/dma-swiotlb.c +++ b/arch/mips/loongson64/common/dma-swiotlb.c @@ -119,6 +119,7 @@ static const struct dma_map_ops loongson_dma_map_ops = { .sync_sg_for_device = loongson_dma_sync_sg_for_device, .mapping_error = swiotlb_dma_mapping_error, .dma_supported = loongson_dma_supported, + .device_is_coherent = plat_device_is_coherent }; void __init plat_swiotlb_setup(void) diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c index c01bd20..6e18301 100644 --- a/arch/mips/mm/dma-default.c +++ b/arch/mips/mm/dma-default.c @@ -407,7 +407,8 @@ static const struct dma_map_ops mips_default_dma_map_ops = { .sync_sg_for_cpu = mips_dma_sync_sg_for_cpu, .sync_sg_for_device = mips_dma_sync_sg_for_device, .mapping_error = mips_dma_mapping_error, - .dma_supported = mips_dma_supported + .dma_supported = mips_dma_supported, + .device_is_coherent = plat_device_is_coherent }; const struct dma_map_ops *mips_dma_map_ops = &mips_default_dma_map_ops; diff --git a/arch/mips/netlogic/common/nlm-dma.c b/arch/mips/netlogic/common/nlm-dma.c index 0ec9d9d..aa11b27 100644 --- a/arch/mips/netlogic/common/nlm-dma.c +++ b/arch/mips/netlogic/common/nlm-dma.c @@ -79,7 +79,8 @@ const struct dma_map_ops nlm_swiotlb_dma_ops = { .sync_sg_for_cpu = swiotlb_sync_sg_for_cpu, .sync_sg_for_device = swiotlb_sync_sg_for_device, .mapping_error = swiotlb_dma_mapping_error, - .dma_supported = swiotlb_dma_supported + .dma_supported = swiotlb_dma_supported, + .device_is_coherent = plat_device_is_coherent }; void __init plat_swiotlb_setup(void) diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 29ce981..08da227 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -131,6 +131,7 @@ struct dma_map_ops { #ifdef ARCH_HAS_DMA_GET_REQUIRED_MASK u64 (*get_required_mask)(struct device *dev); #endif + int (*device_is_coherent)(struct device *dev); int is_phys; }; @@ -697,6 +698,15 @@ static inline void *dma_zalloc_coherent(struct device *dev, size_t size, } #ifdef CONFIG_HAS_DMA +static inline int device_is_coherent(struct device *dev) +{ + const struct dma_map_ops *ops = get_dma_ops(dev); + if (ops && ops->device_is_coherent) + return ops->device_is_coherent(dev); + else + return 1; /* compatible behavior */ +} + static inline int dma_get_cache_alignment(void) { #ifdef ARCH_DMA_MINALIGN
We will use device_is_coherent() as a helper function, which will be used in the next patch. There is a MIPS-specific plat_device_is_coherent(), but we need a more generic solution, so add and use a new function pointer in dma_map_ops. Cc: stable@vger.kernel.org Signed-off-by: Huacai Chen <chenhc@lemote.com> --- arch/mips/cavium-octeon/dma-octeon.c | 3 ++- arch/mips/include/asm/mach-generic/dma-coherence.h | 6 +++--- arch/mips/loongson64/common/dma-swiotlb.c | 1 + arch/mips/mm/dma-default.c | 3 ++- arch/mips/netlogic/common/nlm-dma.c | 3 ++- include/linux/dma-mapping.h | 10 ++++++++++ 6 files changed, 20 insertions(+), 6 deletions(-)