RE: [PATCHv5 16/20] PCI: mobiveil: Add link up condition check

[Z.q. Hou]

Hi Lorenzo,

Thanks a lot for your comments!

> -----Original Message-----
> From: Lorenzo Pieralisi <lorenzo.pieral...@arm.com>
> Sent: 2019年6月12日 1:18
> To: Z.q. Hou <zhiqiang....@nxp.com>; bhelg...@google.com
> Cc: linux-...@vger.kernel.org; linux-arm-ker...@lists.infradead.org;
> devicet...@vger.kernel.org; linux-kernel@vger.kernel.org;
> robh...@kernel.org; mark.rutl...@arm.com; l.subrahma...@mobiveil.co.in;
> shawn...@kernel.org; Leo Li <leoyang...@nxp.com>;
> catalin.mari...@arm.com; will.dea...@arm.com; Mingkai Hu
> <mingkai...@nxp.com>; M.h. Lian <minghuan.l...@nxp.com>; Xiaowei Bao
> <xiaowei....@nxp.com>
> Subject: Re: [PATCHv5 16/20] PCI: mobiveil: Add link up condition check
> 
> NB: Please trim the CC list and keep it to concerned maintainers.
> 
> On Fri, Apr 12, 2019 at 08:36:48AM +0000, Z.q. Hou wrote:
> > From: Hou Zhiqiang <zhiqiang....@nxp.com>
> >
> > Avoid to issue CFG transactions to link partner when the PCIe link is
> > not up.
> >
> > Signed-off-by: Hou Zhiqiang <zhiqiang....@nxp.com>
> > ---
> > V5:
> >  - Corrected the subject.
> >
> >  drivers/pci/controller/pcie-mobiveil.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/pci/controller/pcie-mobiveil.c
> > b/drivers/pci/controller/pcie-mobiveil.c
> > index 621852078caf..1ee3ea2570c0 100644
> > --- a/drivers/pci/controller/pcie-mobiveil.c
> > +++ b/drivers/pci/controller/pcie-mobiveil.c
> > @@ -283,6 +283,10 @@ static bool mobiveil_pcie_valid_device(struct
> > pci_bus *bus, unsigned int devfn)  {
> >     struct mobiveil_pcie *pcie = bus->sysdata;
> >
> > +   /* If there is no link, then there is no device */
> > +   if (bus->number > pcie->root_bus_nr && !mobiveil_pcie_link_up(pcie))
> 
> I think Bjorn mentioned this a million times already, eg:
> 
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Flinux-pci%2F20190411201535.GS256045%40google.com%2F&am
> p;data=02%7C01%7Czhiqiang.hou%40nxp.com%7Cffb4c8dcebe4493a375908
> d6ee90b471%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63695
> 8702637973543&amp;sdata=m%2FqV5zohqyBMUDT7zrVjF%2FLtYeJZO36rdY
> eMTPGGbHg%3D&amp;reserved=0
> 
> this is racy and gives a false sense of robustness. We have code in the kernel
> that checks the link but adding more seems silly to me, so I am inclined to
> drop this patch.
> 

Understand, drop it.

Thanks,
Zhiqiang

> Lorenzo
> 
> > +           return false;
> > +
> >     /* Only one device down on each root port */
> >     if ((bus->number == pcie->root_bus_nr) && (devfn > 0))
> >             return false;
> > --
> > 2.17.1
> >