linux-kernel - Re: [RFC PATCH v2 12/27] damengine: dw-edma: Fix MSI data values for multi-vector IMWr interrupts

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Message-ID: <aS3wo94XbxTCkm25@lizhi-Precision-Tower-5810>
Date: Mon, 1 Dec 2025 14:46:43 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: ntb@...ts.linux.dev, linux-pci@...r.kernel.org,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	mani@...nel.org, kwilczynski@...nel.org, kishon@...nel.org,
	bhelgaas@...gle.com, corbet@....net, vkoul@...nel.org,
	jdmason@...zu.us, dave.jiang@...el.com, allenbh@...il.com,
	Basavaraj.Natikar@....com, Shyam-sundar.S-k@....com,
	kurt.schwemmer@...rosemi.com, logang@...tatee.com,
	jingoohan1@...il.com, lpieralisi@...nel.org, robh@...nel.org,
	jbrunet@...libre.com, fancer.lancer@...il.com, arnd@...db.de,
	pstanner@...hat.com, elfring@...rs.sourceforge.net
Subject: Re: [RFC PATCH v2 12/27] damengine: dw-edma: Fix MSI data values for
 multi-vector IMWr interrupts

On Sun, Nov 30, 2025 at 01:03:50AM +0900, Koichiro Den wrote:
> When multiple MSI vectors are allocated for the DesignWare eDMA, the
> driver currently records the same MSI message for all IRQs by calling
> get_cached_msi_msg() per vector. For multi-vector MSI (as opposed to
> MSI-X), the cached message corresponds to vector 0 and msg.data is
> supposed to be adjusted by the IRQ index.
>
> As a result, all eDMA interrupts share the same MSI data value and the
> interrupt controller cannot distinguish between them.
>
> Introduce dw_edma_compose_msi() to construct the correct MSI message for
> each vector. For MSI-X nothing changes. For multi-vector MSI, derive the
> base IRQ with msi_get_virq(dev, 0) and OR in the per-vector offset into
> msg.data before storing it in dw->irq[i].msi.
>
> This makes each IMWr MSI vector use a unique MSI data value.
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---
>  drivers/dma/dw-edma/dw-edma-core.c | 28 ++++++++++++++++++++++++----
>  1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 8e5f7defa6b6..3542177a4a8e 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -839,6 +839,28 @@ static inline void dw_edma_add_irq_mask(u32 *mask, u32 alloc, u16 cnt)
>  		(*mask)++;
>  }
>
> +static void dw_edma_compose_msi(struct device *dev, int irq, struct msi_msg *out)
> +{
> +	struct msi_desc *desc = irq_get_msi_desc(irq);
> +	struct msi_msg msg;
> +	unsigned int base;
> +
> +	if (!desc)
> +		return;
> +
> +	get_cached_msi_msg(irq, &msg);
> +	if (!desc->pci.msi_attrib.is_msix) {
> +		/*
> +		 * For multi-vector MSI, the cached message corresponds to
> +		 * vector 0. Adjust msg.data by the IRQ index so that each
> +		 * vector gets a unique MSI data value for IMWr Data Register.
> +		 */
> +		base = msi_get_virq(dev, 0);
> +		msg.data |= (irq - base);

why "|=", not "=" here?

Frank

> +	}
> +	*out = msg;
> +}
> +
>  static int dw_edma_irq_request(struct dw_edma *dw,
>  			       u32 *wr_alloc, u32 *rd_alloc)
>  {
> @@ -869,8 +891,7 @@ 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(dev, irq, &dw->irq[0].msi);
>
>  		dw->nr_irqs = 1;
>  	} else {
> @@ -896,8 +917,7 @@ static int dw_edma_irq_request(struct dw_edma *dw,
>  			if (err)
>  				goto err_irq_free;
>
> -			if (irq_get_msi_desc(irq))
> -				get_cached_msi_msg(irq, &dw->irq[i].msi);
> +			dw_edma_compose_msi(dev, irq, &dw->irq[i].msi);
>  		}
>
>  		dw->nr_irqs = i;
> --
> 2.48.1
>