Re: [PATCH v2 02/18] PCI: endpoint: Introduce pci_epc_map_align()

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Sat, Mar 30, 2024 at 01:19:12PM +0900, Damien Le Moal wrote:
> Some endpoint controllers have requirements on the alignment of the
> controller physical memory address that must be used to map a RC PCI
> address region. For instance, the rockchip endpoint controller uses
> at most the lower 20 bits of a physical memory address region as the
> lower bits of an RC PCI address. For mapping a PCI address region of
> size bytes starting from pci_addr, the exact number of address bits
> used is the number of address bits changing in the address range
> [pci_addr..pci_addr + size - 1].
> 
> For this example, this creates the following constraints:
> 1) The offset into the controller physical memory allocated for a
>    mapping depends on the mapping size *and* the starting PCI address
>    for the mapping.
> 2) A mapping size cannot exceed the controller windows size (1MB) minus
>    the offset needed into the allocated physical memory, which can end
>    up being a smaller size than the desired mapping size.
> 
> Handling these constraints independently of the controller being used in
> a PCI EP function driver is not possible with the current EPC API as
> it only provides the ->align field in struct pci_epc_features.
> Furthermore, this alignment is static and does not depend on a mapping
> pci address and size.
> 
> Solve this by introducing the function pci_epc_map_align() and the
> endpoint controller operation ->map_align to allow endpoint function
> drivers to obtain the size and the offset into a controller address
> region that must be used to map an RC PCI address region. The size
> of the physical address region provided by pci_epc_map_align() can then
> be used as the size argument for the function pci_epc_mem_alloc_addr().
> The offset into the allocated controller memory can be used to
> correctly handle data transfers. Of note is that pci_epc_map_align() may
> indicate upon return a mapping size that is smaller (but not 0) than the
> requested PCI address region size. For such case, an endpoint function
> driver must handle data transfers in fragments.
> 

Is there any incentive in exposing pci_epc_map_align()? I mean, why can't it be
hidden inside the new alloc() API itself?

Furthermore, is it possible to avoid the map_align() callback and handle the
alignment within the EPC driver?

- Mani

> The controller operation ->map_align is optional: controllers that do
> not have any address alignment constraints for mapping a RC PCI address
> region do not need to implement this operation. For such controllers,
> pci_epc_map_align() always returns the mapping size as equal
> to the requested size and an offset equal to 0.
> 
> The structure pci_epc_map is introduced to represent a mapping start PCI
> address, size and the size and offset into the controller memory needed
> for mapping the PCI address region.
> 
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> ---
>  drivers/pci/endpoint/pci-epc-core.c | 66 +++++++++++++++++++++++++++++
>  include/linux/pci-epc.h             | 33 +++++++++++++++
>  2 files changed, 99 insertions(+)
> 
> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> index 754afd115bbd..37758ca91d7f 100644
> --- a/drivers/pci/endpoint/pci-epc-core.c
> +++ b/drivers/pci/endpoint/pci-epc-core.c
> @@ -433,6 +433,72 @@ void pci_epc_unmap_addr(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  }
>  EXPORT_SYMBOL_GPL(pci_epc_unmap_addr);
>  
> +/**
> + * pci_epc_map_align() - Get the offset into and the size of a controller memory
> + *			 address region needed to map a RC PCI address region
> + * @epc: the EPC device on which address is allocated
> + * @func_no: the physical endpoint function number in the EPC device
> + * @vfunc_no: the virtual endpoint function number in the physical function
> + * @pci_addr: PCI address to which the physical address should be mapped
> + * @size: the size of the mapping starting from @pci_addr
> + * @map: populate here the actual size and offset into the controller memory
> + *       that must be allocated for the mapping
> + *
> + * Invoke the controller map_align operation to obtain the size and the offset
> + * into a controller address region that must be allocated to map @size
> + * bytes of the RC PCI address space starting from @pci_addr.
> + *
> + * The size of the mapping that can be handled by the controller is indicated
> + * using the pci_size field of @map. This size may be smaller than the requested
> + * @size. In such case, the function driver must handle the mapping using
> + * several fragments. The offset into the controller memory for the effective
> + * mapping of the @pci_addr..@pci_addr+@map->pci_size address range is indicated
> + * using the map_ofst field of @map.
> + */
> +int pci_epc_map_align(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +		      u64 pci_addr, size_t size, struct pci_epc_map *map)
> +{
> +	const struct pci_epc_features *features;
> +	size_t mask;
> +	int ret;
> +
> +	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
> +		return -EINVAL;
> +
> +	if (!size || !map)
> +		return -EINVAL;
> +
> +	memset(map, 0, sizeof(*map));
> +	map->pci_addr = pci_addr;
> +	map->pci_size = size;
> +
> +	if (epc->ops->map_align) {
> +		mutex_lock(&epc->lock);
> +		ret = epc->ops->map_align(epc, func_no, vfunc_no, map);
> +		mutex_unlock(&epc->lock);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Assume a fixed alignment constraint as specified by the controller
> +	 * features.
> +	 */
> +	features = pci_epc_get_features(epc, func_no, vfunc_no);
> +	if (!features || !features->align) {
> +		map->map_pci_addr = pci_addr;
> +		map->map_size = size;
> +		map->map_ofst = 0;

These values are overwritten anyway below.

> +	}
> +
> +	mask = features->align - 1;
> +	map->map_pci_addr = map->pci_addr & ~mask;
> +	map->map_ofst = map->pci_addr & mask;
> +	map->map_size = ALIGN(map->map_ofst + map->pci_size, features->align);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_map_align);
> +
>  /**
>   * pci_epc_map_addr() - map CPU address to PCI address
>   * @epc: the EPC device on which address is allocated
> diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
> index cc2f70d061c8..8cfb4aaf2628 100644
> --- a/include/linux/pci-epc.h
> +++ b/include/linux/pci-epc.h
> @@ -32,11 +32,40 @@ pci_epc_interface_string(enum pci_epc_interface_type type)
>  	}
>  }
>  
> +/**
> + * struct pci_epc_map - information about EPC memory for mapping a RC PCI
> + *                      address range
> + * @pci_addr: start address of the RC PCI address range to map
> + * @pci_size: size of the RC PCI address range to map
> + * @map_pci_addr: RC PCI address used as the first address mapped
> + * @map_size: size of the controller memory needed for the mapping
> + * @map_ofst: offset into the controller memory needed for the mapping
> + * @phys_base: base physical address of the allocated EPC memory
> + * @phys_addr: physical address at which @pci_addr is mapped
> + * @virt_base: base virtual address of the allocated EPC memory
> + * @virt_addr: virtual address at which @pci_addr is mapped
> + */
> +struct pci_epc_map {
> +	phys_addr_t	pci_addr;
> +	size_t		pci_size;
> +
> +	phys_addr_t	map_pci_addr;
> +	size_t		map_size;
> +	phys_addr_t	map_ofst;
> +
> +	phys_addr_t	phys_base;
> +	phys_addr_t	phys_addr;
> +	void __iomem	*virt_base;
> +	void __iomem	*virt_addr;
> +};
> +
>  /**
>   * struct pci_epc_ops - set of function pointers for performing EPC operations
>   * @write_header: ops to populate configuration space header
>   * @set_bar: ops to configure the BAR
>   * @clear_bar: ops to reset the BAR
> + * @map_align: operation to get the size and offset into a controller memory
> + *             window needed to map an RC PCI address region
>   * @map_addr: ops to map CPU address to PCI address
>   * @unmap_addr: ops to unmap CPU address and PCI address
>   * @set_msi: ops to set the requested number of MSI interrupts in the MSI
> @@ -61,6 +90,8 @@ struct pci_epc_ops {
>  			   struct pci_epf_bar *epf_bar);
>  	void	(*clear_bar)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  			     struct pci_epf_bar *epf_bar);
> +	int	(*map_align)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +			    struct pci_epc_map *map);
>  	int	(*map_addr)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  			    phys_addr_t addr, u64 pci_addr, size_t size);
>  	void	(*unmap_addr)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> @@ -234,6 +265,8 @@ int pci_epc_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  		    struct pci_epf_bar *epf_bar);
>  void pci_epc_clear_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  		       struct pci_epf_bar *epf_bar);
> +int pci_epc_map_align(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +		      u64 pci_addr, size_t size, struct pci_epc_map *map);
>  int pci_epc_map_addr(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  		     phys_addr_t phys_addr,
>  		     u64 pci_addr, size_t size);
> -- 
> 2.44.0
> 

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