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: <immlt7jck44hs5srgmodjnghufivfxpok7r4gfdhoqnfzx3omx@6yvdjmoahjwh>
Date: Thu, 18 Dec 2025 15:52:27 +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 Tue, Dec 02, 2025 at 03:32:49PM +0900, Koichiro Den wrote:
> 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.

I forgot to add a follow-up comment before sending RFC v3. Here I was too
distracted, it was intentional to apply OR to the base value, which was
cached. So [RFC PATCH v3 10/35] remains unchanged.
https://lore.kernel.org/all/20251217151609.3162665-11-den@valinux.co.jp/

Thanks,
Koichiro

> 
> 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
> > >