Messages in this thread Patch in this message |  | | Subject | Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma() | From | John Hubbard <> | Date | Sun, 2 May 2021 14:23:31 -0700 |
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On 4/8/21 10:01 AM, Logan Gunthorpe wrote: > dma_map_sg() either returns a positive number indicating the number > of entries mapped or zero indicating that resources were not available > to create the mapping. When zero is returned, it is always safe to retry > the mapping later once resources have been freed. > > Once P2PDMA pages are mixed into the SGL there may be pages that may > never be successfully mapped with a given device because that device may > not actually be able to access those pages. Thus, multiple error > conditions will need to be distinguished to determine weather a retry > is safe. > > Introduce dma_map_sg_p2pdma[_attrs]() with a different calling > convention from dma_map_sg(). The function will return a positive > integer on success or a negative errno on failure. > > ENOMEM will be used to indicate a resource failure and EREMOTEIO to > indicate that a P2PDMA page is not mappable. > > The __DMA_ATTR_PCI_P2PDMA attribute is introduced to inform the lower > level implementations that P2PDMA pages are allowed and to warn if a > caller introduces them into the regular dma_map_sg() interface. > > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- > include/linux/dma-mapping.h | 15 +++++++++++ > kernel/dma/mapping.c | 52 ++++++++++++++++++++++++++++++++----- > 2 files changed, 61 insertions(+), 6 deletions(-) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 2a984cb4d1e0..50b8f586cf59 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -60,6 +60,12 @@ > * at least read-only at lesser-privileged levels). > */ > #define DMA_ATTR_PRIVILEGED (1UL << 9) > +/* > + * __DMA_ATTR_PCI_P2PDMA: This should not be used directly, use > + * dma_map_sg_p2pdma() instead. Used internally to indicate that the > + * caller is using the dma_map_sg_p2pdma() interface. > + */ > +#define __DMA_ATTR_PCI_P2PDMA (1UL << 10) >
As mentioned near the top of this file, Documentation/core-api/dma-attributes.rst also needs to be updated, for this new item.
> /* > * A dma_addr_t can hold any valid DMA or bus address for the platform. It can > @@ -107,6 +113,8 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size, > enum dma_data_direction dir, unsigned long attrs); > int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > enum dma_data_direction dir, unsigned long attrs); > +int dma_map_sg_p2pdma_attrs(struct device *dev, struct scatterlist *sg, > + int nents, enum dma_data_direction dir, unsigned long attrs); > void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg, > int nents, enum dma_data_direction dir, > unsigned long attrs); > @@ -160,6 +168,12 @@ static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, > { > return 0; > } > +static inline int dma_map_sg_p2pdma_attrs(struct device *dev, > + struct scatterlist *sg, int nents, enum dma_data_direction dir, > + unsigned long attrs) > +{ > + return 0; > +} > static inline void dma_unmap_sg_attrs(struct device *dev, > struct scatterlist *sg, int nents, enum dma_data_direction dir, > unsigned long attrs) > @@ -392,6 +406,7 @@ static inline void dma_sync_sgtable_for_device(struct device *dev, > #define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, 0) > #define dma_unmap_single(d, a, s, r) dma_unmap_single_attrs(d, a, s, r, 0) > #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0) > +#define dma_map_sg_p2pdma(d, s, n, r) dma_map_sg_p2pdma_attrs(d, s, n, r, 0)
This hunk is fine, of course.
But, about pre-existing issues: note to self, or to anyone: send a patch to turn these into inline functions. The macro redirection here is not adding value, but it does make things just a little bit worse.
> #define dma_unmap_sg(d, s, n, r) dma_unmap_sg_attrs(d, s, n, r, 0) > #define dma_map_page(d, p, o, s, r) dma_map_page_attrs(d, p, o, s, r, 0) > #define dma_unmap_page(d, a, s, r) dma_unmap_page_attrs(d, a, s, r, 0) > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c > index b6a633679933..923089c4267b 100644 > --- a/kernel/dma/mapping.c > +++ b/kernel/dma/mapping.c > @@ -177,12 +177,8 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size, > } > EXPORT_SYMBOL(dma_unmap_page_attrs); > > -/* > - * dma_maps_sg_attrs returns 0 on error and > 0 on success. > - * It should never return a value < 0. > - */
It would be better to leave the comment in place, given the non-standard return values. However, looking around here, it would be better if we go with the standard -ERRNO for error, and >0 for sucess.
There are pre-existing BUG_ON() and WARN_ON_ONCE() items that are partly an attempt to compensate for not being able to return proper -ERRNO codes. For example, this:
BUG_ON(!valid_dma_direction(dir));
...arguably should be more like this:
if(WARN_ON_ONCE(!valid_dma_direction(dir))) return -EINVAL;
> -int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > - enum dma_data_direction dir, unsigned long attrs) > +static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, > + int nents, enum dma_data_direction dir, unsigned long attrs) > { > const struct dma_map_ops *ops = get_dma_ops(dev); > int ents; > @@ -197,6 +193,20 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > ents = dma_direct_map_sg(dev, sg, nents, dir, attrs); > else > ents = ops->map_sg(dev, sg, nents, dir, attrs); > + > + return ents; > +} > + > +/* > + * dma_maps_sg_attrs returns 0 on error and > 0 on success. > + * It should never return a value < 0. > + */ > +int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > + enum dma_data_direction dir, unsigned long attrs) > +{ > + int ents;
Pre-existing note, feel free to ignore: the ents and nents in the same routines together, are way too close to the each other in naming. Maybe using "requested_nents", or "nents_arg", for the incoming value, would help.
> + > + ents = __dma_map_sg_attrs(dev, sg, nents, dir, attrs); > BUG_ON(ents < 0); > debug_dma_map_sg(dev, sg, nents, ents, dir); > > @@ -204,6 +214,36 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > } > EXPORT_SYMBOL(dma_map_sg_attrs); > > +/* > + * like dma_map_sg_attrs, but returns a negative errno on error (and > 0 > + * on success). This function must be used if PCI P2PDMA pages might > + * be in the scatterlist.
Let's turn this into a kernel doc comment block, seeing as how it clearly wants to be--you're almost there already. You've even reinvented @Return, below. :)
> + * > + * On error this function may return: > + * -ENOMEM indicating that there was not enough resources available and > + * the transfer may be retried later > + * -EREMOTEIO indicating that P2PDMA pages were included but cannot > + * be mapped by the specified device, retries will always fail > + * > + * The scatterlist should be unmapped with the regular dma_unmap_sg[_attrs]().
How about:
"The scatterlist should be unmapped via dma_unmap_sg[_attrs]()."
> + */ > +int dma_map_sg_p2pdma_attrs(struct device *dev, struct scatterlist *sg, > + int nents, enum dma_data_direction dir, unsigned long attrs) > +{ > + int ents; > + > + ents = __dma_map_sg_attrs(dev, sg, nents, dir, > + attrs | __DMA_ATTR_PCI_P2PDMA); > + if (!ents) > + ents = -ENOMEM; > + > + if (ents > 0) > + debug_dma_map_sg(dev, sg, nents, ents, dir); > + > + return ents; > +} > +EXPORT_SYMBOL_GPL(dma_map_sg_p2pdma_attrs); > + > void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg, > int nents, enum dma_data_direction dir, > unsigned long attrs) >
thanks, -- John Hubbard NVIDIA
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