[v3,13/18] dmaengine: dma-jz4780: Set DTCn register explicitly
diff mbox

Message ID 20180721110643.19624-14-paul@crapouillou.net
State Changes Requested
Headers show

Commit Message

Paul Cercueil July 21, 2018, 11:06 a.m. UTC
From: Daniel Silsby <dansilsby@gmail.com>

Normally, we wouldn't set the channel transfer count register directly
when using descriptor-driven transfers. However, there is no harm in
doing so, and it allows jz4780_dma_desc_residue() to report the correct
residue of an ongoing transfer, no matter when it is called.

Signed-off-by: Daniel Silsby <dansilsby@gmail.com>
Tested-by: Mathieu Malaterre <malat@debian.org>
---
 drivers/dma/dma-jz4780.c | 9 +++++++++
 1 file changed, 9 insertions(+)

 v2: No change

 v3: No change

Comments

Randy Dunlap July 21, 2018, 3:10 p.m. UTC | #1
On 07/21/2018 04:06 AM, Paul Cercueil wrote:
> From: Daniel Silsby <dansilsby@gmail.com>
> 
> Normally, we wouldn't set the channel transfer count register directly
> when using descriptor-driven transfers. However, there is no harm in
> doing so, and it allows jz4780_dma_desc_residue() to report the correct
> residue of an ongoing transfer, no matter when it is called.
> 
> Signed-off-by: Daniel Silsby <dansilsby@gmail.com>
> Tested-by: Mathieu Malaterre <malat@debian.org>
> ---
>  drivers/dma/dma-jz4780.c | 9 +++++++++
>  1 file changed, 9 insertions(+)

Hi,

Documentation/process/submitting-patches.rst says:

The Signed-off-by: tag indicates that the signer was involved in the
development of the patch, or that he/she was in the patch's delivery path.

That means that patches that are from Daniel but you send (delivery path)
should also be Signed-off-by: you.

Patch
diff mbox

diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
index cc2a86844db4..78849131c81d 100644
--- a/drivers/dma/dma-jz4780.c
+++ b/drivers/dma/dma-jz4780.c
@@ -530,6 +530,15 @@  static void jz4780_dma_begin(struct jz4780_dma_chan *jzchan)
 	jz4780_dma_chn_writel(jzdma, jzchan->id, JZ_DMA_REG_DRT,
 			      jzchan->transfer_type);
 
+	/*
+	 * Set the transfer count. This is redundant for a descriptor-driven
+	 * transfer. However, there can be a delay between the transfer start
+	 * time and when DTCn reg contains the new transfer count. Setting
+	 * it explicitly ensures residue is computed correctly at all times.
+	 */
+	jz4780_dma_chn_writel(jzdma, jzchan->id, JZ_DMA_REG_DTC,
+				jzchan->desc->desc[jzchan->curr_hwdesc].dtc);
+
 	/* Write descriptor address and initiate descriptor fetch. */
 	desc_phys = jzchan->desc->desc_phys +
 		    (jzchan->curr_hwdesc * sizeof(*jzchan->desc->desc));