Re: [PATCH 10/23] dmaengine: sdxi: Complete administrative context jump start

[Frank Li]

On Fri, Apr 10, 2026 at 08:07:20AM -0500, Nathan Lynch wrote:
> Now that the SDXI function has been placed in active state, the admin
> context can finally be started by writing its doorbell. Introduce
> sdxi_cxt_push_doorbell() to pair the necessary barrier with the
> doorbell update.
>
> Co-developed-by: Wei Huang <wei.huang2@xxxxxxx>
> Signed-off-by: Wei Huang <wei.huang2@xxxxxxx>
> Signed-off-by: Nathan Lynch <nathan.lynch@xxxxxxx>
> ---
>  drivers/dma/sdxi/context.c |  8 ++++++++
>  drivers/dma/sdxi/context.h |  2 ++
>  drivers/dma/sdxi/device.c  | 15 ++++++++++++++-
>  3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/sdxi/context.c b/drivers/dma/sdxi/context.c
> index 097d871e530f..934c487b4774 100644
> --- a/drivers/dma/sdxi/context.c
> +++ b/drivers/dma/sdxi/context.c
> @@ -16,6 +16,7 @@
>  #include <linux/dmapool.h>
>  #include <linux/errno.h>
>  #include <linux/iommu.h>
> +#include <linux/io-64-nonatomic-lo-hi.h>
>  #include <linux/slab.h>
>  #include <linux/types.h>
>  #include <asm/barrier.h>
> @@ -258,6 +259,13 @@ static int sdxi_publish_cxt(const struct sdxi_cxt *cxt)
>  	/* todo: need to send DSC_CXT_UPD to admin */
>  }
>
> +void sdxi_cxt_push_doorbell(struct sdxi_cxt *cxt, u64 index)
> +{
> +	/* Ensure preceding write index increment is visible. */
> +	dma_wmb();

Needn't barrier(), iowrite64() should make sure previous write complete.

See Documentation/memory-barriers.txt

Frank
> +	iowrite64(index, cxt->db);
> +}
> +
>  static void free_admin_cxt(void *ptr)
>  {
>  	struct sdxi_dev *sdxi = ptr;
> diff --git a/drivers/dma/sdxi/context.h b/drivers/dma/sdxi/context.h
> index bbde1fd49af3..c34acd730acb 100644
> --- a/drivers/dma/sdxi/context.h
> +++ b/drivers/dma/sdxi/context.h
> @@ -58,4 +58,6 @@ struct sdxi_cxt {
>
>  int sdxi_admin_cxt_init(struct sdxi_dev *sdxi);
>
> +void sdxi_cxt_push_doorbell(struct sdxi_cxt *cxt, u64 index);
> +
>  #endif /* DMA_SDXI_CONTEXT_H */
> diff --git a/drivers/dma/sdxi/device.c b/drivers/dma/sdxi/device.c
> index 145aa098c269..15f61d1ce490 100644
> --- a/drivers/dma/sdxi/device.c
> +++ b/drivers/dma/sdxi/device.c
> @@ -244,7 +244,20 @@ static int sdxi_fn_activate(struct sdxi_dev *sdxi)
>  	 * SDXI 1.0 4.1.8.9: Set MMIO_CTL0.fn_gsr to GSRV_ACTIVE and
>  	 * wait for MMIO_STS0.fn_gsv to reach GSV_ACTIVE or GSV_ERROR.
>  	 */
> -	return sdxi_dev_start(sdxi);
> +	err = sdxi_dev_start(sdxi);
> +	if (err)
> +		return err;
> +
> +	/*
> +	 * SDXI 1.0 4.1.8.10.b: Start the admin context using method
> +	 * #3 ("Jump Start 1") from 4.3.4 Starting A Context and
> +	 * Context Signaling. We haven't queued any descriptors to the
> +	 * admin context at this point, so the appropriate value for
> +	 * the doorbell is 0.
> +	 */
> +	sdxi_cxt_push_doorbell(sdxi->admin_cxt, 0);
> +
> +	return 0;
>  }
>
>  static int sdxi_create_dma_pool(struct sdxi_dev *sdxi, struct dma_pool **pool,
>
> --
> 2.53.0
>