Re: [PATCH v3 10/24] dmaengine: dw-edma: Prepare LL kicks for event serialization

[Frank Li]

On Tue, Jul 28, 2026 at 02:03:09AM +0900, Koichiro Den wrote:
> Both eDMA and HDMA perform the same remote LL read-back immediately
> before writing the doorbell register.
>
> A later patch serializes each LL doorbell write against IRQ event
> capture with a raw spinlock. Keeping the read-back in the provider
> callback would hold that lock across a remote read. Move the common
> read-back into a core kick helper, where it can run before the
> serialized section, and leave dw_edma_core_ch_maybe_doorbell() to decide
> whether a kick is needed.
>
> No functional change.
>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---
> Changes in v3:
>   - New prep patch split from "Centralize LL doorbell decisions" to keep
>     that policy change focused and the remote LL read-back outside the
>     event lock added later. (Sashiko)
>
>  drivers/dma/dw-edma/dw-edma-core.c    | 20 +++++++++++++++++++-
>  drivers/dma/dw-edma/dw-edma-v0-core.c | 16 ----------------
>  drivers/dma/dw-edma/dw-hdma-v0-core.c | 16 ----------------
>  3 files changed, 19 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index bb57f2d39d1c..e3d0559206d8 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -13,6 +13,7 @@
>  #include <linux/dmaengine.h>
>  #include <linux/err.h>
>  #include <linux/interrupt.h>
> +#include <linux/io.h>
>  #include <linux/irq.h>
>  #include <linux/dma/edma.h>
>  #include <linux/dma-mapping.h>
> @@ -254,6 +255,23 @@ static void dw_edma_finish_termination(struct dw_edma_chan *chan)
>  	chan->status = EDMA_ST_IDLE;
>  }
>
> +static void dw_edma_core_ll_sync(struct dw_edma_chan *chan)
> +{
> +	/*
> +	 * Remote controller registers and LL memory may be reached through
> +	 * different paths. Complete posted LL writes before the doorbell.
> +	 */
> +	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
> +		readl(chan->ll_region.vaddr.io);
> +}
> +
> +/* Must be called with vc.lock held for an LL channel. */
> +static void dw_edma_core_ch_kick(struct dw_edma_chan *chan)
> +{
> +	dw_edma_core_ll_sync(chan);
> +	dw_edma_core_ch_doorbell(chan);
> +}
> +

Can you move

	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
		readl(chan->ll_region.vaddr.io);

into funciton dw_edma_core_ch_doorbell().

Frank
>  /* Must be called with vc.lock held. */
>  static void dw_edma_core_ch_maybe_doorbell(struct dw_edma_chan *chan)
>  {
> @@ -261,7 +279,7 @@ static void dw_edma_core_ch_maybe_doorbell(struct dw_edma_chan *chan)
>  	    chan->status != EDMA_ST_BUSY || !dw_edma_ll_pending(chan))
>  		return;
>
> -	dw_edma_core_ch_doorbell(chan);
> +	dw_edma_core_ch_kick(chan);
>  }
>
>  static void dw_edma_device_caps(struct dma_chan *dchan,
> diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
> index d883ca446f5a..b3098eb83442 100644
> --- a/drivers/dma/dw-edma/dw-edma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
> @@ -480,20 +480,6 @@ static void dw_edma_v0_core_ch_enable(struct dw_edma_chan *chan)
>  		  upper_32_bits(chan->ll_region.paddr));
>  }
>
> -static void dw_edma_v0_sync_ll_data(struct dw_edma_chan *chan)
> -{
> -	/*
> -	 * In case of remote eDMA engine setup, the DW PCIe RP/EP internal
> -	 * configuration registers and application memory are normally accessed
> -	 * over different buses. Ensure LL-data reaches the memory before the
> -	 * doorbell register is toggled by issuing the dummy-read from the remote
> -	 * LL memory in a hope that the MRd TLP will return only after the
> -	 * last MWr TLP is completed
> -	 */
> -	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
> -		readl(chan->ll_region.vaddr.io);
> -}
> -
>  static void dw_edma_v0_core_ch_config(struct dw_edma_chan *chan)
>  {
>  	struct dw_edma *dw = chan->dw;
> @@ -624,8 +610,6 @@ static void dw_edma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
>  {
>  	struct dw_edma *dw = chan->dw;
>
> -	dw_edma_v0_sync_ll_data(chan);
> -
>  	/* Doorbell */
>  	SET_RW_32(dw, chan->dir, doorbell,
>  		  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));
> diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> index afc2f24fecd3..64a07fbc5be3 100644
> --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> @@ -282,20 +282,6 @@ static void dw_hdma_v0_core_ch_enable(struct dw_edma_chan *chan)
>  		  HDMA_V0_CONSUMER_CYCLE_STAT | HDMA_V0_CONSUMER_CYCLE_BIT);
>  }
>
> -static void dw_hdma_v0_sync_ll_data(struct dw_edma_chan *chan)
> -{
> -	/*
> -	 * In case of remote HDMA engine setup, the DW PCIe RP/EP internal
> -	 * configuration registers and application memory are normally accessed
> -	 * over different buses. Ensure LL-data reaches the memory before the
> -	 * doorbell register is toggled by issuing the dummy-read from the remote
> -	 * LL memory in a hope that the MRd TLP will return only after the
> -	 * last MWr TLP is completed
> -	 */
> -	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
> -		readl(chan->ll_region.vaddr.io);
> -}
> -
>  static void dw_hdma_v0_core_non_ll_start(struct dw_edma_chan *chan,
>  					 struct dw_edma_burst *child)
>  {
> @@ -393,8 +379,6 @@ static void dw_hdma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
>  {
>  	struct dw_edma *dw = chan->dw;
>
> -	dw_hdma_v0_sync_ll_data(chan);
> -
>  	/* Doorbell */
>  	SET_CH_32(dw, chan->dir, chan->id, doorbell, HDMA_V0_DOORBELL_START);
>  }
> --
> 2.51.0
>