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

[Frank Li]

On Sat, Aug 29, 2026 at 01:36:11AM +0900, Koichiro Den wrote:
> 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@xxxxxxxxxxxxx>
> ---
> Changes in v2:
>   - Rework v1 patch 5 for an MSI allocation shared with vNTB.
>     https://lore.kernel.org/r/20260312165005.1148676-6-den@xxxxxxxxxxxxx/
>
>  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);

where this function? I missed dependence?

Frank
>
>  		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
>