[Intel-wired-lan] [PATCH v5 03/14] PCI: Add pcie_bandwidth_capable() to compute max supported link bandwidth

[Keller, Jacob E]

> -----Original Message-----
> From: Bjorn Helgaas [mailto:helgaas at kernel.org]
> Sent: Tuesday, April 03, 2018 7:06 AM
> To: Jacob Keller <jacob.keller at gmail.com>
> Cc: Tal Gilboa <talgi at mellanox.com>; Tariq Toukan <tariqt at mellanox.com>;
> Keller, Jacob E <jacob.e.keller at intel.com>; Ariel Elior <ariel.elior at cavium.com>;
> Ganesh Goudar <ganeshgr at chelsio.com>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher at intel.com>; everest-linux-l2 at cavium.com; intel-wired-
> lan at lists.osuosl.org; netdev at vger.kernel.org; linux-kernel at vger.kernel.org;
> linux-pci at vger.kernel.org
> Subject: Re: [PATCH v5 03/14] PCI: Add pcie_bandwidth_capable() to compute
> max supported link bandwidth
> 
> On Mon, Apr 02, 2018 at 05:30:54PM -0700, Jacob Keller wrote:
> > On Mon, Apr 2, 2018 at 7:05 AM, Bjorn Helgaas <helgaas at kernel.org> wrote:
> > > +/* PCIe speed to Mb/s reduced by encoding overhead */
> > > +#define PCIE_SPEED2MBS_ENC(speed) \
> > > +       ((speed) == PCIE_SPEED_16_0GT ? (16000*(128/130)) : \
> > > +        (speed) == PCIE_SPEED_8_0GT  ?  (8000*(128/130)) : \
> > > +        (speed) == PCIE_SPEED_5_0GT  ?  (5000*(8/10)) : \
> > > +        (speed) == PCIE_SPEED_2_5GT  ?  (2500*(8/10)) : \
> > > +        0)
> > > +
> >
> > Should this be "(speed * x ) / y" instead? wouldn't they calculate
> > 128/130 and truncate that to zero before multiplying by the speed? Or
> > are compilers smart enough to do this the other way to avoid the
> > losses?
> 
> Yep, thanks for saving me yet more embarrassment.

That's what patch review is for :D

Thanks,
Jake