Subject: Re: [PATCH] forcedeth: msi interrupts

From: Ayaz Abdulla <[email-masked]>
Date: Fri, 06 Jun 2008 13:15:32 -0400

Andrew Morton wrote:
> On Tue, 03 Jun 2008 16:51:46 -0400
> Ayaz Abdulla <[email-masked]> wrote:
> 
>  > This patch adds a workaround for lost MSI interrupts. There is a race
>  > condition in the HW in which future interrupts could be missed. The
>  > workaround is to toggle the MSI irq mask.
>  >
> 
> Do you think this is a 2.6.26 thing?
It is by HW design, not related to the kernel.

> 
>  > [patch-forcedeth-msi-irq  text/plain (1.3KB)]
>  > --- old/drivers/net/forcedeth.c       2008-06-03 16:16:26.000000000 -0400
>  > +++ new/drivers/net/forcedeth.c       2008-06-03 16:31:44.000000000 -0400
>  > @@ -3277,6 +3277,20 @@
>  >       dprintk(KERN_DEBUG "%s: link change notification done.\n", 
> dev->name);
>  >  }
>  > 
>  > +static inline void nv_msi_workaround(struct net_device *dev)
>  > +{
>  > +     struct fe_priv *np = netdev_priv(dev);
>  > +     u8 __iomem *base = get_hwbase(dev);
>  > +
>  > +     /* Need to toggle the msi irq mask within the ethernet device,
>  > +      * otherwise, future interrupts will not be detected.
>  > +      */
>  > +     if (np->msi_flags & NV_MSI_ENABLED) {
>  > +             writel(0, base + NvRegMSIIrqMask);
>  > +             writel(NVREG_MSI_VECTOR_0_ENABLED, base + NvRegMSIIrqMask);
>  > +     }
>  > +}
>  > +
>  >  static irqreturn_t nv_nic_irq(int foo, void *data)
>  >  {
>  >       struct net_device *dev = (struct net_device *) data;
>  > @@ -3299,6 +3313,8 @@
>  >               if (!(events & np->irqmask))
>  >                       break;
>  > 
>  > +             nv_msi_workaround(dev);
>  > +
>  >               spin_lock(&np->lock);
>  >               nv_tx_done(dev);
>  >               spin_unlock(&np->lock);
>  > @@ -3414,6 +3430,8 @@
>  >               if (!(events & np->irqmask))
>  >                       break;
>  > 
>  > +             nv_msi_workaround(dev);
>  > +
>  >               spin_lock(&np->lock);
>  >               nv_tx_done_optimized(dev, TX_WORK_PER_LOOP);
>  >               spin_unlock(&np->lock);
>  > @@ -3754,6 +3772,8 @@
>  >       if (!(events & NVREG_IRQ_TIMER))
>  >               return IRQ_RETVAL(0);
>  > 
>  > +     nv_msi_workaround(dev);
>  > +
>  >       spin_lock(&np->lock);
>  >       np->intr_test = 1;
>  >       spin_unlock(&np->lock);
>  >
> 
> I'm not loving the implementation.
> 
> - That `inline' adds 35 bytes more text to the driver, and we expect
>   that this often yields slower code.
> 
> - Every caller of nv_msi_workaround() already has the fe_priv* in a
>   local variable, so why not pass that in and save the additional
>   pointer calculation?
> 
> So this:
> 
> diff -puN drivers/net/forcedeth.c~forcedeth-msi-interrupts-uninlining 
> drivers/net/forcedeth.c
> --- a/drivers/net/forcedeth.c~forcedeth-msi-interrupts-uninlining
> +++ a/drivers/net/forcedeth.c
> @@ -3277,15 +3277,14 @@ static void nv_link_irq(struct net_devic
>         dprintk(KERN_DEBUG "%s: link change notification done.\n", 
> dev->name);
>  }
> 
> -static inline void nv_msi_workaround(struct net_device *dev)
> +static void nv_msi_workaround(struct fe_priv *np)
>  {
> -       struct fe_priv *np = netdev_priv(dev);
> -       u8 __iomem *base = get_hwbase(dev);
> -
>         /* Need to toggle the msi irq mask within the ethernet device,
>          * otherwise, future interrupts will not be detected.
>          */
>         if (np->msi_flags & NV_MSI_ENABLED) {
> +               u8 __iomem *base = np->base;
> +
>                 writel(0, base + NvRegMSIIrqMask);
>                 writel(NVREG_MSI_VECTOR_0_ENABLED, base + NvRegMSIIrqMask);
>         }
> @@ -3313,7 +3312,7 @@ static irqreturn_t nv_nic_irq(int foo, v
>                 if (!(events & np->irqmask))
>                         break;
> 
> -               nv_msi_workaround(dev);
> +               nv_msi_workaround(np);
> 
>                 spin_lock(&np->lock);
>                 nv_tx_done(dev);
> @@ -3430,7 +3429,7 @@ static irqreturn_t nv_nic_irq_optimized(
>                 if (!(events & np->irqmask))
>                         break;
> 
> -               nv_msi_workaround(dev);
> +               nv_msi_workaround(np);
> 
>                 spin_lock(&np->lock);
>                 nv_tx_done_optimized(dev, TX_WORK_PER_LOOP);
> @@ -3772,7 +3771,7 @@ static irqreturn_t nv_nic_irq_test(int f
>         if (!(events & NVREG_IRQ_TIMER))
>                 return IRQ_RETVAL(0);
> 
> -       nv_msi_workaround(dev);
> +       nv_msi_workaround(np);
> 
>         spin_lock(&np->lock);
>         np->intr_test = 1;
> _
> 
> 
> save 42 bytes of text.
> 
> Now, if the (np->msi_flags & NV_MSI_ENABLED) test is usually false then
> there might be some advantage in inlining the whole thing.  Or just
> inlining the NV_MSI_ENABLED test, but those two writel()s probably
> aren't worth the fuss of uninlining.
> 
> 
Sure, thats fine.

> 
> Semi-relatedly, the driver does an awful lot of this:
> 
>         struct fe_priv *np = get_nvpriv(dev);
>         u8 __iomem *base = get_hwbase(dev);
> 
> but get_hwbase() re-evaluates netdev_priv().  It would be more
> efficient to pass an fe_priv* into get_hwbase().  Or, better, just
> remove get_hwbase() and open-code `np->base' everywhere.
> 
> 
> 

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