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: <n77eybnm2lyzujpwlszcd4dlfxvs44scedvh2rzlity25svlq4@2vucqeqby2op>
Date: Tue, 2 Dec 2025 15:32:49 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Frank Li <Frank.li@....com>
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 Mon, Dec 01, 2025 at 02:46:43PM -0500, Frank Li wrote:
> 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?

"=" is better and safe here. Thanks for pointing it out, I'll fix it.

Koichiro

> 
> 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
> >