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[PATCH v3 5/6] dmaengine: dw-edma: HDMA: Add sync read before starting the DMA transfer in remote setup

Kory Maincent posted 6 patches 2 years, 2 months ago
There is a newer version of this series
[PATCH v3 5/6] dmaengine: dw-edma: HDMA: Add sync read before starting the DMA transfer in remote setup
Posted by Kory Maincent 2 years, 2 months ago 
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
---
 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 04b0bcb6ded9..13b6aec6a6de 100644
--- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
@@ -222,6 +222,20 @@ 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;
@@ -252,6 +266,9 @@ 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
Re: [PATCH v3 5/6] dmaengine: dw-edma: HDMA: Add sync read before starting the DMA transfer in remote setup
Posted by Serge Semin 2 years, 2 months ago 
On Wed, Oct 11, 2023 at 10:11:44AM +0200, Kory Maincent wrote:
> 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.

s/can appears/may occur

> In remote setup we can only use a readl to the memory to assured the full
> write has occurred.

s/assured/assure

> 
> Fixes: e74c39573d35 ("dmaengine: dw-edma: Add support for native HDMA")
> Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>

Reviewed-by: Serge Semin <fancer.lancer@gmail.com>

-Serge(y)

> ---
> 
> 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(+)
> 
> diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> index 04b0bcb6ded9..13b6aec6a6de 100644
> --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> @@ -222,6 +222,20 @@ 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;
> @@ -252,6 +266,9 @@ 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
>
Re: [PATCH v3 5/6] dmaengine: dw-edma: HDMA: Add sync read before starting the DMA transfer in remote setup
Posted by Serge Semin 2 years, 2 months ago 
On Wed, Oct 11, 2023 at 01:47:49PM +0300, Serge Semin wrote:
> On Wed, Oct 11, 2023 at 10:11:44AM +0200, Kory Maincent wrote:
> > 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.
> 
> s/can appears/may occur

It should have been: s/can appears/will occur

-Serge(y)

> 
> > In remote setup we can only use a readl to the memory to assured the full
> > write has occurred.
> 
> s/assured/assure
> 
> > 
> > Fixes: e74c39573d35 ("dmaengine: dw-edma: Add support for native HDMA")
> > Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
> 
> Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
> 
> -Serge(y)
> 
> > ---
> > 
> > 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(+)
> > 
> > diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> > index 04b0bcb6ded9..13b6aec6a6de 100644
> > --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> > +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> > @@ -222,6 +222,20 @@ 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;
> > @@ -252,6 +266,9 @@ 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
> >

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