[PATCH 5/6] PCI: imx6: Force Gen1 operation

[Zhu Richard-R65037]

Hi Marek:

> -----Original Message-----
[...]
> > > ---
> > >
> > >  drivers/pci/host/pci-imx6.c | 13 ++++++++++++-
> > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/pci/host/pci-imx6.c
> > > b/drivers/pci/host/pci-imx6.c index ca8c5de..8402e9a 100644
> > > --- a/drivers/pci/host/pci-imx6.c
> > > +++ b/drivers/pci/host/pci-imx6.c
> > > @@ -321,6 +321,7 @@ static void imx6_pcie_host_init(struct pcie_port
> > > *pp)
> > >
> > >  {
> > >
> > >  	int count = 0;
> > >  	struct imx6_pcie *imx6_pcie = to_imx6_pcie(pp);
> > >
> > > +	uint32_t tmp;
> > >
> > >  	imx6_pcie_assert_core_reset(pp);
> > >
> > > @@ -330,13 +331,23 @@ static void imx6_pcie_host_init(struct
> > > pcie_port
> > > *pp)
> > >
> > >  	dw_pcie_setup_rc(pp);
> > >
> > > +	/*
> > > +	 * FIXME:
> > > +	 * Force Gen1 operation. In case the IP block is in Gen2 operation
> > > +	 * mode, it does not detect the PCIe switch at all.
> > > +	 */
> > > +	tmp = readl(pp->dbi_base + 0x7c);
> > > +	tmp &= ~0xf;
> > > +	tmp |= 0x1;
> > > +	writel(tmp, pp->dbi_base + 0x7c);
> > > +
> >
> > Since you are forcing RC to work in GEN1, so you will not be able to
> > connect any device at GEN2 now.
> 
> I'd rather prefer to know WHY if the RC is operating in Gen2 mode by default,
> I cannot see the PCIe switch (Pericom PI7C9X2G303) connected to it. I was
> unable to figure this out. Tim pointed out this thread [1] , so it might be
> related in some way.
> 
> [1] https://community.freescale.com/message/316162#316162
> 
> I tried switching the PCIe RC to Gen2 operation right after LinkUp by writing
> this register with 0x2 again and re-issuing the LinkUp check, which passed and
> the status register reported Gen2 operation, but then the PCIe Intel NIC
> connected to the downstream port of the Pericom switch still reported Gen1
> operation for some reason.
> 
 [Richard] Is your Inetl NIC GEN1 EP device?

> > Yes, There are some buggy PCIe devices which works with GEN1 only host.
> 
> The pericom one is Gen2 according to it's datasheet.
[Richard] Yes, it is. Pericom's PI7C9X2G303EL is GEN2 PCIe switch.
It had been verified on FSL's 3.0.35 releases.

> 
> > So better solution should be to initialize RC by default at GEN2 or
> > highest speed. Further, a parameter say gen_only can be passed from DT
> > to force GEN1 only mode.
> >
> > What do you say?
> 
> I say I'd like to know the root cause of this problem. This Gen2 fix was
> pulled from one of the myriad variants of the FSL PCIe driver, so apparently
> this issue happens to other people as well. But why and how to properly fix
> this so the whole PCIe bus does operate in Gen2 mode, I cannot tell :-(
[Richard] GEN2 mode had been verified in FSL 3.0.35 kernel releases before.
I don't know why it can't work in GEN2 mode in the latest kernel.
BTW, Based on for-next branch of shawn's git reops and applied Merak's patch-set,
 my PI7C9X2G303EL with intel e1000e network card plugged can't be detected at all. :(.

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Best Regards
Richard Zhu