linux-kernel - [PATCH 7/7] dmaengine: sh: rz-dmac: Set the Link End (LE) bit on the last descriptor

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Message-ID: <20260126103155.2644586-8-claudiu.beznea.uj@bp.renesas.com>
Date: Mon, 26 Jan 2026 12:31:55 +0200
From: Claudiu <claudiu.beznea@...on.dev>
To: vkoul@...nel.org,
	biju.das.jz@...renesas.com,
	prabhakar.mahadev-lad.rj@...renesas.com,
	lgirdwood@...il.com,
	broonie@...nel.org,
	perex@...ex.cz,
	tiwai@...e.com,
	p.zabel@...gutronix.de,
	geert+renesas@...der.be,
	fabrizio.castro.jz@...esas.com
Cc: claudiu.beznea@...on.dev,
	dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-sound@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: [PATCH 7/7] dmaengine: sh: rz-dmac: Set the Link End (LE) bit on the last descriptor

From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

On an RZ/G2L-based system, it has been observed that when the DMA channels
for all enabled IPs are active (TX and RX for one serial IP, TX and RX for
one audio IP, and TX and RX for one SPI IP), shortly after all of them are
started, the system can become irrecoverably blocked. In one debug session
the system did not block, and the DMA HW registers were inspected. It was
found that the DER (Descriptor Error) bit in the CHSTAT register for one of
the SPI DMA channels was set.

According to the RZ/G2L HW Manual, Rev. 1.30, chapter 14.4.7 Channel
Status Register n/nS (CHSTAT_n/nS), description of the DER bit, the DER
bit is set when the LV (Link Valid) value loaded with a descriptor in link
mode is 0. This means that the DMA engine has loaded an invalid
descriptor (as defined in Table 14.14, Header Area, of the same manual).

The same chapter states that when a descriptor error occurs, the transfer
is stopped, but no DMA error interrupt is generated.

Set the LE bit on the last descriptor of a transfer. This informs the DMA
engine that this is the final descriptor for the transfer.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
---
 drivers/dma/sh/rz-dmac.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/sh/rz-dmac.c b/drivers/dma/sh/rz-dmac.c
index 8f3e2719e639..3a77a560fcd5 100644
--- a/drivers/dma/sh/rz-dmac.c
+++ b/drivers/dma/sh/rz-dmac.c
@@ -206,6 +206,7 @@ struct rz_dmac {

 /* LINK MODE DESCRIPTOR */
 #define HEADER_LV			BIT(0)
+#define HEADER_LE			BIT(1)
 #define HEADER_WBD			BIT(2)

 #define RZ_DMAC_MAX_CHAN_DESCRIPTORS	16
@@ -383,7 +384,7 @@ static void rz_dmac_prepare_desc_for_memcpy(struct rz_dmac_chan *channel)
 	lmdesc->chcfg = chcfg;
 	lmdesc->chitvl = 0;
 	lmdesc->chext = 0;
-	lmdesc->header = HEADER_LV;
+	lmdesc->header = HEADER_LV | HEADER_LE;

 	rz_dmac_set_dma_req_no(dmac, channel->index, dmac->info->default_dma_req_no);

@@ -425,7 +426,7 @@ static void rz_dmac_prepare_descs_for_slave_sg(struct rz_dmac_chan *channel)
 		lmdesc->chext = 0;
 		if (i == (sg_len - 1)) {
 			lmdesc->chcfg = (channel->chcfg & ~CHCFG_DEM);
-			lmdesc->header = HEADER_LV;
+			lmdesc->header = HEADER_LV | HEADER_LE;
 		} else {
 			lmdesc->chcfg = channel->chcfg;
 			lmdesc->header = HEADER_LV;
-- 
2.43.0