Re: [PATCH v2 4/5] dmaengine: dw-edma: HDMA: Add sync read before starting the DMA transfer in remote setup

Serge Semin
2023-10-03T15:20:33Z

On Tue, Oct 03, 2023 at 02:15:42PM +0200, Köry Maincent wrote:
> From: Kory Maincent <kory.maincent@bootlin.com>
>
> The Linked list element and pointer are not stored in the same memory as
> the HDMA controller register. If the doorbell register is toggled before
> the full write of the linked list a race condition error can appears.
> In remote setup we can only use a readl to the memory to assured the full
> write has occurred.
>
> Fixes: e74c39573d35 ("dmaengine: dw-edma: Add support for native HDMA")
> Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
> ---
>
> Changes in v2:
> - Move the sync read in a function.
> - Add commments

Note you need to resubmit the entire series if any of its part has
changed. So please add these patches to your patchset (in place of the
4/5 and 5/5 patches I commented) and resend it as v3.

-Serge(y)

> ---
> drivers/dma/dw-edma/dw-hdma-v0-core.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> index 0cce1880cfdc..9109dd6c2e76 100644
> --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> @@ -221,6 +221,20 @@ static void dw_hdma_v0_core_write_chunk(struct dw_edma_chunk *chunk)
> dw_hdma_v0_write_ll_link(chunk, i, control, chunk->ll_region.paddr);
> }
>
> +static void dw_hdma_v0_sync_ll_data(struct dw_edma_chunk *chunk)
> +{
> + /*
> + * In case of remote HDMA engine setup, the DW PCIe RP/EP internals
> + * 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 posted MRd TLP will return only after the
> + * last MWr TLP is completed
> + */
> + if (!(chunk->chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
> + readl(chunk->ll_region.vaddr.io);
> +}
> +
> static void dw_hdma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
> {
> struct dw_edma_chan *chan = chunk->chan;
> @@ -251,6 +265,9 @@ static void dw_hdma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
> /* Set consumer cycle */
> SET_CH_32(dw, chan->dir, chan->id, cycle_sync,
> HDMA_V0_CONSUMER_CYCLE_STAT | HDMA_V0_CONSUMER_CYCLE_BIT);
> +
> + dw_hdma_v0_sync_ll_data(chunk);
> +
> /* Doorbell */
> SET_CH_32(dw, chan->dir, chan->id, doorbell, HDMA_V0_DOORBELL_START);
> }
> --
> 2.25.1
>