Re: [PATCH v4 15/25] dmaengine: sdxi: Per-context access key (AKey) table entry allocator

[Frank Li <Frank.li@oss.nxp.com>]

On Tue, Nov 03, 2026 at 08:49:56PM -0600, 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 DMAengine provider uses one AKey for copy-buffer access and completion
> interrupts.
>
> Co-developed-by: Wei Huang <wei.huang2@amd.com>
> Signed-off-by: Wei Huang <wei.huang2@amd.com>
> Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>
> ---

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>  drivers/dma/sdxi/context.c |  3 +++
>  drivers/dma/sdxi/context.h | 24 ++++++++++++++++++++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/drivers/dma/sdxi/context.c b/drivers/dma/sdxi/context.c
> index b26eec3805fb..956bb06f9499 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/slab.h>
>  #include <linux/types.h>
> @@ -57,6 +58,7 @@ static void sdxi_free_cxt(struct sdxi_cxt *cxt)
>  				  cxt->akey_table, cxt->akey_table_dma);
>  	if (cxt->sq)
>  		sdxi_sq_free(sdxi, cxt->sq);
> +	ida_destroy(&cxt->akey_ida);
>  	kfree(cxt->ring_state);
>  	kfree(cxt);
>  }
> @@ -73,6 +75,7 @@ static struct sdxi_cxt *sdxi_alloc_cxt(struct sdxi_dev *sdxi)
>  		return NULL;
>
>  	cxt->sdxi = sdxi;
> +	ida_init(&cxt->akey_ida);
>
>  	cxt->ring_state = kzalloc_obj(*cxt->ring_state, GFP_KERNEL);
>  	if (!cxt->ring_state)
> diff --git a/drivers/dma/sdxi/context.h b/drivers/dma/sdxi/context.h
> index 14ce4f5f9b74..cad5a153ec22 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"
> @@ -32,6 +35,7 @@ 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;
>
> @@ -54,4 +58,24 @@ static inline bool sdxi_cxt_is_admin(const struct sdxi_cxt *cxt)
>  	return cxt == to_admin_cxt(cxt);
>  }
>
> +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 */
>
> --
> 2.56.0
>