RE: [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@xxxxxxxxxx]
> Sent: Tuesday, April 03, 2018 7:06 AM
> To: Jacob Keller <jacob.keller@xxxxxxxxx>
> Cc: Tal Gilboa <talgi@xxxxxxxxxxxx>; Tariq Toukan <tariqt@xxxxxxxxxxxx>;
> Keller, Jacob E <jacob.e.keller@xxxxxxxxx>; Ariel Elior <ariel.elior@xxxxxxxxxx>;
> Ganesh Goudar <ganeshgr@xxxxxxxxxxx>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher@xxxxxxxxx>; everest-linux-l2@xxxxxxxxxx; intel-wired-
> lan@xxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-pci@xxxxxxxxxxxxxxx
> 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@xxxxxxxxxx> 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