[PATCH v2 3/3] dmaengine: dw-edma: Account for the MSI vector offset

[Koichiro Den <den@valinux.co.jp>]

get_cached_msi_msg() returns the base message shared by a multi-MSI
descriptor. dw-edma currently derives per-channel data from its local IRQ
index and does not adjust a common IRQ at all. Both assume eDMA starts at
the descriptor's first vector.

That is not true when eDMA receives a tail subset. Compose each message
from the IRQ offset relative to the descriptor base in both paths.

While at it, avoid reading PCI MSI attributes from descriptors owned by
non-PCI devices.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
Changes in v2:
  - Rework v1 patch 5 for an MSI allocation shared with vNTB.
    https://lore.kernel.org/r/20260312165005.1148676-6-den@valinux.co.jp/

 drivers/dma/dw-edma/dw-edma-core.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index a8c6bd508fcd..6af8a414e4a2 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/module.h>
+#include <linux/pci.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
@@ -1075,12 +1076,23 @@ static inline void dw_edma_dec_irq_alloc(int *nr_irqs, u32 *alloc, u16 cnt)
 	}
 }
 
+static void dw_edma_compose_msi(int irq, struct msi_msg *msi)
+{
+	struct msi_desc *desc = irq_get_msi_desc(irq);
+
+	if (!desc)
+		return;
+
+	get_cached_msi_msg(irq, msi);
+	if (dev_is_pci(desc->dev) && !desc->pci.msi_attrib.is_msix)
+		msi->data += irq - desc->irq;
+}
+
 static int dw_edma_irq_request(struct dw_edma *dw,
 			       u32 *wr_alloc, u32 *rd_alloc)
 {
 	struct dw_edma_chip *chip = dw->chip;
 	struct device *dev = dw->chip->dev;
-	struct msi_desc *msi_desc;
 	int i, err = 0;
 	u32 ch_cnt;
 	int irq;
@@ -1105,8 +1117,7 @@ static int dw_edma_irq_request(struct dw_edma *dw,
 			return err;
 		}
 
-		if (irq_get_msi_desc(irq))
-			get_cached_msi_msg(irq, &dw->irq[0].msi);
+		dw_edma_compose_msi(irq, &dw->irq[0].msi);
 
 		dw->nr_irqs = 1;
 	} else {
@@ -1129,12 +1140,7 @@ static int dw_edma_irq_request(struct dw_edma *dw,
 					  &dw->irq[i]);
 			if (err)
 				goto err_irq_free;
-			msi_desc = irq_get_msi_desc(irq);
-			if (msi_desc) {
-				get_cached_msi_msg(irq, &dw->irq[i].msi);
-				if (!msi_desc->pci.msi_attrib.is_msix)
-					dw->irq[i].msi.data = dw->irq[0].msi.data + i;
-			}
+			dw_edma_compose_msi(irq, &dw->irq[i].msi);
 		}
 
 		dw->nr_irqs = i;
-- 
2.51.0