Re: [PATCH v8 20/23] PCI/P2PDMA: Let a client declare that it selects ATS per mapping

[Thomas Hellström]

On Mon, 2026-09-28 at 14:19 +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@xxxxxxxxxx>
> 
> The PCIe ATS Enable bit covers the whole device, so P2PDMA cannot
> tell
> from it whether a client will translate a given address. Most devices
> translate any address once ATS is enabled, but some choose ATS per
> DMA
> mapping and can still use bus addresses for the rest.
> 
> Add pcim_p2pdma_set_ats_per_mapping() so the driver of such a device
> can
> declare that before P2PDMA starts treating clients with ATS enabled
> as
> translating everything. Keep it in the device's P2PDMA state, which
> already ends with the driver binding.
> 
> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
Reviewed-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>

> ---
>  drivers/pci/p2pdma.c       | 27 +++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h |  4 ++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 1f4bf0125a5c..ae676509f9f3 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -26,6 +26,7 @@
>  struct pci_p2pdma {
>  	struct gen_pool *pool;
>  	bool p2pmem_published;
> +	bool ats_per_mapping;
>  	struct xarray map_types;
>  	struct p2pdma_provider mem[PCI_STD_NUM_BARS];
>  };
> @@ -1568,6 +1569,32 @@ void pci_p2pmem_publish(struct pci_dev *pdev,
> bool publish)
>  }
>  EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
>  
> +/**
> + * pcim_p2pdma_set_ats_per_mapping - Declare per-mapping ATS for a
> client
> + * @pdev: PCI device that initiates peer-to-peer DMA
> + *
> + * Declare that @pdev issues Translated Requests only for the DMA
> mappings its
> + * driver sets up to use ATS, rather than for any address once ATS
> is enabled.
> + * P2PDMA then takes the Address Type of this client's Requests from
> the TLP
> + * flags its callers pass.
> + */
> +void pcim_p2pdma_set_ats_per_mapping(struct pci_dev *pdev)
> +{
> +	struct pci_p2pdma *p2p;
> +
> +	p2p = rcu_dereference_protected(pdev->p2pdma, 1);
> +	if (!p2p)
> +		/*
> +		 * ats_per_mapping is a performance optimization,
> +		 * if pcim_p2pdma_init() didn't set pdev->p2pdma
> pointer
> +		 * for some reason, let's simply use ATS global
> settings.
> +		 */
> +		return;
> +
> +	p2p->ats_per_mapping = true;
> +}
> +EXPORT_SYMBOL_GPL(pcim_p2pdma_set_ats_per_mapping);
> +
>  /**
>   * pci_p2pdma_map_type_tlp - Determine the mapping type for P2PDMA
> transfers
>   * @provider: P2PDMA provider structure
> diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
> index 36045b1b730c..543a09426a11 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -109,6 +109,7 @@ struct scatterlist *pci_p2pmem_alloc_sgl(struct
> pci_dev *pdev,
>  					 unsigned int *nents, u32
> length);
>  void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist
> *sgl);
>  void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
> +void pcim_p2pdma_set_ats_per_mapping(struct pci_dev *pdev);
>  int pci_p2pdma_enable_store(const char *page, struct pci_dev
> **p2p_dev,
>  			    bool *use_p2pdma);
>  ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
> @@ -166,6 +167,9 @@ static inline void pci_p2pmem_free_sgl(struct
> pci_dev *pdev,
>  static inline void pci_p2pmem_publish(struct pci_dev *pdev, bool
> publish)
>  {
>  }
> +static inline void pcim_p2pdma_set_ats_per_mapping(struct pci_dev
> *pdev)
> +{
> +}
>  static inline int pci_p2pdma_enable_store(const char *page,
>  		struct pci_dev **p2p_dev, bool *use_p2pdma)
>  {