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Re: [PATCH RFC 50/77] mlx5: Update MSI/MSI-X interrupts enablement code

To: Eli Cohen <eli@dev.mellanox.co.il>
Subject: Re: [PATCH RFC 50/77] mlx5: Update MSI/MSI-X interrupts enablement code
From: Alexander Gordeev <agordeev@redhat.com>
Date: Thu, 3 Oct 2013 21:48:39 +0200
Cc: linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>, Ralf Baechle <ralf@linux-mips.org>, Michael Ellerman <michael@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>, Dan Williams <dan.j.williams@intel.com>, Andy King <acking@vmware.com>, Jon Mason <jon.mason@intel.com>, Matt Porter <mporter@kernel.crashing.org>, linux-pci@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux390@de.ibm.com, linux-s390@vger.kernel.org, x86@kernel.org, linux-ide@vger.kernel.org, iss_storagedev@hp.com, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, e1000-devel@lists.sourceforge.net, linux-driver@qlogic.com, Solarflare linux maintainers <linux-net-drivers@solarflare.com>, "VMware, Inc." <pv-drivers@vmware.com>, linux-scsi@vger.kernel.org
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References: <cover.1380703262.git.agordeev@redhat.com> <9650a7dfbcfd5f1da21f7b093665abf4b1041071.1380703263.git.agordeev@redhat.com> <20131003071433.GA7299@mtldesk30>
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On Thu, Oct 03, 2013 at 10:14:33AM +0300, Eli Cohen wrote:
> On Wed, Oct 02, 2013 at 12:49:06PM +0200, Alexander Gordeev wrote:
> >  
> > +   err = pci_msix_table_size(dev->pdev);
> > +   if (err < 0)
> > +           return err;
> > +
> >     nvec = dev->caps.num_ports * num_online_cpus() + MLX5_EQ_VEC_COMP_BASE;
> >     nvec = min_t(int, nvec, num_eqs);
> > +   nvec = min_t(int, nvec, err);
> >     if (nvec <= MLX5_EQ_VEC_COMP_BASE)
> >             return -ENOSPC;
> 
> Making sure we don't request more vectors then the device's is capable
> of -- looks good.
> >  
> > @@ -131,20 +136,15 @@ static int mlx5_enable_msix(struct mlx5_core_dev *dev)
> >     for (i = 0; i < nvec; i++)
> >             table->msix_arr[i].entry = i;
> >  
> > -retry:
> > -   table->num_comp_vectors = nvec - MLX5_EQ_VEC_COMP_BASE;
> >     err = pci_enable_msix(dev->pdev, table->msix_arr, nvec);
> > -   if (err <= 0) {
> > +   if (err) {
> > +           kfree(table->msix_arr);
> >             return err;
> > -   } else if (err > MLX5_EQ_VEC_COMP_BASE) {
> > -           nvec = err;
> > -           goto retry;
> >     }
> >  
> 
> According to latest sources, pci_enable_msix() may still fail so why
> do you want to remove this code?

pci_enable_msix() may fail, but it can not return a positive number.

We first calculate how many MSI-Xs we need, adjust to what we can get,
check if that is enough and only then go for it.

> > -   mlx5_core_dbg(dev, "received %d MSI vectors out of %d requested\n", 
> > err, nvec);
> > -   kfree(table->msix_arr);
> > +   table->num_comp_vectors = nvec - MLX5_EQ_VEC_COMP_BASE;
> >  
> > -   return -ENOSPC;
> > +   return 0;
> >  }
> >  
> >  static void mlx5_disable_msix(struct mlx5_core_dev *dev)

-- 
Regards,
Alexander Gordeev
agordeev@redhat.com

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