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

Commit Message

Kory Maincent Oct. 3, 2023, 12:15 p.m. UTC

From: Kory Maincent <[e-mail]>

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 <[e-mail]>
---

Changes in v2:
- Move the sync read in a function.
- Add commments
---
 drivers/dma/dw-edma/dw-hdma-v0-core.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Comments

Serge Semin Oct. 3, 2023, 3:20 p.m. UTC | #1

On Tue, Oct 03, 2023 at 02:15:42PM +0200, Köry Maincent wrote:
> From: Kory Maincent <[e-mail]>
> 
> 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 <[e-mail]>
> ---
> 
> 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
>

Kory Maincent Oct. 3, 2023, 3:34 p.m. UTC | #2

On Tue, 3 Oct 2023 18:20:23 +0300
Serge Semin <[e-mail]> wrote:

> On Tue, Oct 03, 2023 at 02:15:42PM +0200, Köry Maincent wrote:
> > From: Kory Maincent <[e-mail]>
> > 
> > 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 <[e-mail]>
> > ---
> > 
> > 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.

Alright.
Should I wait for Cai's response for patch 1/5 before sending v3. He seems to
never having woken up in our discussions.

Serge Semin Oct. 3, 2023, 3:57 p.m. UTC | #3

On Tue, Oct 03, 2023 at 05:34:32PM +0200, Köry Maincent wrote:
> On Tue, 3 Oct 2023 18:20:23 +0300
> Serge Semin <[e-mail]> wrote:
> 
> > On Tue, Oct 03, 2023 at 02:15:42PM +0200, Köry Maincent wrote:
> > > From: Kory Maincent <[e-mail]>
> > > 
> > > 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 <[e-mail]>
> > > ---
> > > 
> > > 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.
> 
> Alright.
> Should I wait for Cai's response for patch 1/5 before sending v3. He seems to
> never having woken up in our discussions.

Ok. Let's wait for Cai for sometime. We are in the middle of the
dev-cycle anyway so no reason to rush.

-Serge(y)

Patch

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);
 }