Re: [PATCH RFC 1/2] scatterlist: add I/O variant of sg_pcopy & sg_copy

[Robin Murphy <robin.murphy@arm.com>]

On 2021-06-28 13:34, Neil Armstrong wrote:
> When copying from/to an iomem mapped memory, the current sg_copy & sg_pcopy can't
> be used and lead to local variants in drivers like in [1] & [2].
> 
> This introduces an I/O variant to be used instead of the local variants.
> 
> [1] mv_cesa_sg_copy in drivers/crypto/marvell/cesa/tdma.c
> [2] meson_mmc_copy_buffer in drivers/mmc/host/meson-gx-mmc.c

Other than one apparent typo below, this looks like what I imagined, 
thanks for putting it together!

> Cc: Robin Murphy <robin.murphy@arm.com>
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> ---
>   include/linux/scatterlist.h |  14 +++++
>   lib/scatterlist.c           | 119 ++++++++++++++++++++++++++++++++++++
>   2 files changed, 133 insertions(+)
> 
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 6f70572b2938..6ef339ba5290 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -308,15 +308,29 @@ void sgl_free(struct scatterlist *sgl);
>   size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
>   		      size_t buflen, off_t skip, bool to_buffer);
>   
> +size_t sg_copy_io(struct scatterlist *sgl, unsigned int nents, void __iomem *buf,
> +		  size_t buflen, off_t skip, bool to_buffer);
> +
>   size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
>   			   const void *buf, size_t buflen);
>   size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
>   			 void *buf, size_t buflen);
>   
> +size_t sg_copy_from_io(struct scatterlist *sgl, unsigned int nents,
> +		       const void __iomem *buf, size_t buflen);
> +size_t sg_copy_to_io(struct scatterlist *sgl, unsigned int nents,
> +		     void __iomem *buf, size_t buflen);
> +
>   size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
>   			    const void *buf, size_t buflen, off_t skip);
>   size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
>   			  void *buf, size_t buflen, off_t skip);
> +
> +size_t sg_pcopy_from_io(struct scatterlist *sgl, unsigned int nents,
> +			const void __iomem *buf, size_t buflen, off_t skip);
> +size_t sg_pcopy_to_io(struct scatterlist *sgl, unsigned int nents,
> +		      void __iomem *buf, size_t buflen, off_t skip);
> +
>   size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
>   		       size_t buflen, off_t skip);
>   
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index a59778946404..e52f37b181fa 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -954,6 +954,55 @@ size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
>   }
>   EXPORT_SYMBOL(sg_copy_buffer);
>   
> +/**
> + * sg_copy_io - Copy data between an I/O mapped buffer and an SG list
> + * @sgl:		 The SG list
> + * @nents:		 Number of SG entries
> + * @buf:		 Where to copy from
> + * @buflen:		 The number of bytes to copy
> + * @skip:		 Number of bytes to skip before copying
> + * @to_buffer:		 transfer direction (true == from an sg list to a
> + *			 buffer, false == from a buffer to an sg list)
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_copy_io(struct scatterlist *sgl, unsigned int nents, void __iomem *buf,
> +		  size_t buflen, off_t skip, bool to_buffer)
> +{
> +	unsigned int offset = 0;
> +	struct sg_mapping_iter miter;
> +	unsigned int sg_flags = SG_MITER_ATOMIC;
> +
> +	if (to_buffer)
> +		sg_flags |= SG_MITER_FROM_SG;
> +	else
> +		sg_flags |= SG_MITER_TO_SG;
> +
> +	sg_miter_start(&miter, sgl, nents, sg_flags);
> +
> +	if (!sg_miter_skip(&miter, skip))
> +		return 0;
> +
> +	while ((offset < buflen) && sg_miter_next(&miter)) {
> +		unsigned int len;
> +
> +		len = min(miter.length, buflen - offset);
> +
> +		if (to_buffer)
> +			memcpy_toio(buf + offset, miter.addr, len);
> +		else
> +			memcpy_fromio(miter.addr, buf + offset, len);
> +
> +		offset += len;
> +	}
> +
> +	sg_miter_stop(&miter);
> +
> +	return offset;
> +}
> +EXPORT_SYMBOL(sg_copy_io);
> +
>   /**
>    * sg_copy_from_buffer - Copy from a linear buffer to an SG list
>    * @sgl:		 The SG list
> @@ -988,6 +1037,40 @@ size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
>   }
>   EXPORT_SYMBOL(sg_copy_to_buffer);
>   
> +/**
> + * sg_copy_from_io - Copy from an I/O mapped buffer to an SG list
> + * @sgl:		 The SG list
> + * @nents:		 Number of SG entries
> + * @buf:		 Where to copy from
> + * @buflen:		 The number of bytes to copy
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_copy_from_io(struct scatterlist *sgl, unsigned int nents,
> +		       const void *buf, size_t buflen)

The __iomem annotation wants to be on buf here raher than cast in below, 
to match the prototype (and everything else).

Cheers,
Robin.

> +{
> +	return sg_copy_io(sgl, nents, (void __iomem *)buf, buflen, 0, false);
> +}
> +EXPORT_SYMBOL(sg_copy_from_io);
> +
> +/**
> + * sg_copy_to_io - Copy from an SG list to an I/O mapped buffer
> + * @sgl:		 The SG list
> + * @nents:		 Number of SG entries
> + * @buf:		 Where to copy to
> + * @buflen:		 The number of bytes to copy
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_copy_to_io(struct scatterlist *sgl, unsigned int nents,
> +		     void __iomem *buf, size_t buflen)
> +{
> +	return sg_copy_io(sgl, nents, buf, buflen, 0, true);
> +}
> +EXPORT_SYMBOL(sg_copy_to_io);
> +
>   /**
>    * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
>    * @sgl:		 The SG list
> @@ -1024,6 +1107,42 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
>   }
>   EXPORT_SYMBOL(sg_pcopy_to_buffer);
>   
> +/**
> + * sg_pcopy_from_io - Copy from an I/O mapped buffer to an SG list
> + * @sgl:		 The SG list
> + * @nents:		 Number of SG entries
> + * @buf:		 Where to copy from
> + * @buflen:		 The number of bytes to copy
> + * @skip:		 Number of bytes to skip before copying
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_pcopy_from_io(struct scatterlist *sgl, unsigned int nents,
> +			const void __iomem *buf, size_t buflen, off_t skip)
> +{
> +	return sg_copy_io(sgl, nents, (void __iomem *)buf, buflen, skip, false);
> +}
> +EXPORT_SYMBOL(sg_pcopy_from_io);
> +
> +/**
> + * sg_pcopy_to_io - Copy from an SG list to an I/O mapped buffer
> + * @sgl:		 The SG list
> + * @nents:		 Number of SG entries
> + * @buf:		 Where to copy to
> + * @buflen:		 The number of bytes to copy
> + * @skip:		 Number of bytes to skip before copying
> + *
> + * Returns the number of copied bytes.
> + *
> + **/
> +size_t sg_pcopy_to_io(struct scatterlist *sgl, unsigned int nents,
> +		      void __iomem *buf, size_t buflen, off_t skip)
> +{
> +	return sg_copy_io(sgl, nents, buf, buflen, skip, true);
> +}
> +EXPORT_SYMBOL(sg_pcopy_to_io);
> +
>   /**
>    * sg_zero_buffer - Zero-out a part of a SG list
>    * @sgl:		 The SG list
>