dmaengine: dw-edma: eDMA: Add sync read before starting the DMA transfer in remote...

The Linked list element and pointer are not stored in the same memory as
the eDMA controller register. If the doorbell register is toggled before
the full write of the linked list a race condition error will occur.
In remote setup we can only use a readl to the memory to assure the full
write has occurred.

Fixes: 7e4b8a4fbe2c ("dmaengine: Add Synopsys eDMA IP version 0 support")
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Link: https://lore.kernel.org/r/20240129-b4-feature_hdma_mainline-v7-6-8e8c1acb7a46@bootlin.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
index b38786f0ad7995d9b0d22aa18fdd6d2407320c26..b75fdaffad9a4ea6cd8d15e8f43bea550848b46c 100644 (file)
--- a/drivers/dma/dw-edma/dw-edma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
@@ -346,6 +346,20 @@ static void dw_edma_v0_core_write_chunk(struct dw_edma_chunk *chunk)
        dw_edma_v0_write_ll_link(chunk, i, control, chunk->ll_region.paddr);
 }
 
+static void dw_edma_v0_sync_ll_data(struct dw_edma_chunk *chunk)
+{
+       /*
+        * 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 (!(chunk->chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
+               readl(chunk->ll_region.vaddr.io);
+}
+
 static void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
 {
        struct dw_edma_chan *chan = chunk->chan;
@@ -412,6 +426,9 @@ static void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
                SET_CH_32(dw, chan->dir, chan->id, llp.msb,
                          upper_32_bits(chunk->ll_region.paddr));
        }
+
+       dw_edma_v0_sync_ll_data(chunk);
+
        /* Doorbell */
        SET_RW_32(dw, chan->dir, doorbell,
                  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));