Re: [PATCH 15/23] dmaengine: sdxi: Per-context access key (AKey) table entry allocator

[Frank Li]

On Fri, Apr 10, 2026 at 08:07:25AM -0500, Nathan Lynch wrote:
> Each SDXI context has a table of access keys (AKeys). SDXI descriptors
> submitted to a context may refer to an AKey associated with that
> context by its index in the table. AKeys describe properties of the
> access that the descriptor is to perform, such as PASID or a target
> SDXI function, or an interrupt to trigger.
>
> Use a per-context IDA to keep track of used entries in the table.
> Provide sdxi_alloc_akey(), which claims an AKey table entry for the
> caller to program directly; sdxi_akey_index(), which returns the
> entry's index for programming into descriptors the caller intends to
> submit; and sdxi_free_akey(), which clears the entry and makes it
> available again.
>
> The DMA engine provider is currently the only user and allocates a
> single entry that encodes the access properties for copy operations
> and a completion interrupt. More complex use patterns are possible
> when user space gains access to SDXI contexts (not in this series).
>
> Co-developed-by: Wei Huang <wei.huang2@xxxxxxx>
> Signed-off-by: Wei Huang <wei.huang2@xxxxxxx>
> Signed-off-by: Nathan Lynch <nathan.lynch@xxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/dma/sdxi/context.c |  5 +++++
>  drivers/dma/sdxi/context.h | 24 ++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
>
> diff --git a/drivers/dma/sdxi/context.c b/drivers/dma/sdxi/context.c
> index 792b5032203b..04e0d3e6a337 100644
> --- a/drivers/dma/sdxi/context.c
> +++ b/drivers/dma/sdxi/context.c
> @@ -15,6 +15,7 @@
>  #include <linux/dma-mapping.h>
>  #include <linux/dmapool.h>
>  #include <linux/errno.h>
> +#include <linux/idr.h>
>  #include <linux/iommu.h>
>  #include <linux/io-64-nonatomic-lo-hi.h>
>  #include <linux/slab.h>
> @@ -61,6 +62,7 @@ static void sdxi_free_cxt(struct sdxi_cxt *cxt)
>  		dma_free_coherent(sdxi_to_dev(sdxi), sq->ring_size,
>  				  sq->desc_ring, sq->ring_dma);
>  	kfree(cxt->sq);
> +	ida_destroy(&cxt->akey_ida);
>  	kfree(cxt->ring_state);
>  	kfree(cxt);
>  }
> @@ -381,6 +383,7 @@ int sdxi_admin_cxt_init(struct sdxi_dev *sdxi)
>  	cxt->db = sdxi->dbs + cxt->id * sdxi->db_stride;
>  	sdxi_ring_state_init(cxt->ring_state, &sq->cxt_sts->read_index,
>  			     sq->write_index, sq->ring_entries, sq->desc_ring);
> +	ida_init(&cxt->akey_ida);
>
>  	err = sdxi_publish_cxt(cxt);
>  	if (err)
> @@ -406,6 +409,8 @@ struct sdxi_cxt *sdxi_cxt_new(struct sdxi_dev *sdxi)
>  	sq = cxt->sq;
>  	sdxi_ring_state_init(cxt->ring_state, &sq->cxt_sts->read_index,
>  			     sq->write_index, sq->ring_entries, sq->desc_ring);
> +	ida_init(&cxt->akey_ida);
> +
>  	if (register_cxt(sdxi, cxt))
>  		return NULL;
>
> diff --git a/drivers/dma/sdxi/context.h b/drivers/dma/sdxi/context.h
> index 9779b9aa4f86..5310e51a668c 100644
> --- a/drivers/dma/sdxi/context.h
> +++ b/drivers/dma/sdxi/context.h
> @@ -6,7 +6,10 @@
>  #ifndef DMA_SDXI_CONTEXT_H
>  #define DMA_SDXI_CONTEXT_H
>
> +#include <linux/array_size.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/idr.h>
> +#include <linux/string.h>
>  #include <linux/types.h>
>
>  #include "hw.h"
> @@ -50,6 +53,7 @@ struct sdxi_cxt {
>  	struct sdxi_cxt_ctl *cxt_ctl;
>  	dma_addr_t cxt_ctl_dma;
>
> +	struct ida akey_ida;
>  	struct sdxi_akey_table *akey_table;
>  	dma_addr_t akey_table_dma;
>
> @@ -75,4 +79,24 @@ static inline bool sdxi_cxt_is_admin(const struct sdxi_cxt *cxt)
>
>  void sdxi_cxt_push_doorbell(struct sdxi_cxt *cxt, u64 index);
>
> +static inline struct sdxi_akey_ent *sdxi_alloc_akey(struct sdxi_cxt *cxt)
> +{
> +	unsigned int max = ARRAY_SIZE(cxt->akey_table->entry) - 1;
> +	int idx = ida_alloc_max(&cxt->akey_ida, max, GFP_KERNEL);
> +
> +	return idx < 0 ? NULL : &cxt->akey_table->entry[idx];
> +}
> +
> +static inline unsigned int sdxi_akey_index(const struct sdxi_cxt *cxt,
> +					   const struct sdxi_akey_ent *akey)
> +{
> +	return akey - &cxt->akey_table->entry[0];
> +}
> +
> +static inline void sdxi_free_akey(struct sdxi_cxt *cxt, struct sdxi_akey_ent *akey)
> +{
> +	memset(akey, 0, sizeof(*akey));
> +	ida_free(&cxt->akey_ida, sdxi_akey_index(cxt, akey));
> +}
> +
>  #endif /* DMA_SDXI_CONTEXT_H */
>
> --
> 2.53.0
>