Re: [PATCH] PCI: mediatek-gen3: fix PCIe #PERST being de-asserted too early

[Jianjun Wang (王建军)]

On Tue, 2023-10-10 at 18:42 +0200, Frank Wunderlich wrote:
>  	 
> External email : Please do not click links or open attachments until
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> Am 10. Oktober 2023 18:04:23 MESZ schrieb Bjorn Helgaas <
> helgaas@xxxxxxxxxx>:
> > On Fri, Oct 06, 2023 at 09:45:58AM +0200, Daniel Golle wrote:
> > > The driver for MediaTek gen3 PCIe hosts de-asserts all reset
> > > signals at the same time using a single register write operation.
> > > Delay the de-assertion of the #PERST signal by 100ms as required
> > > by
> > > PCIe CEM clause 2.2, some PCIe devices fail to come up otherwise.
> > > 
> > > Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
> > >  drivers/pci/controller/pcie-mediatek-gen3.c | 8 +++++++-
> > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c
> > > b/drivers/pci/controller/pcie-mediatek-gen3.c
> > > index e0e27645fdf4..ba8cfce03aad 100644
> > > --- a/drivers/pci/controller/pcie-mediatek-gen3.c
> > > +++ b/drivers/pci/controller/pcie-mediatek-gen3.c
> > > @@ -350,7 +350,13 @@ static int mtk_pcie_startup_port(struct
> > > mtk_gen3_pcie *pcie)
> > > 
> > 
> > I feel like I'm missing something because this patch seems to be
> > adding a delay for T_PVPERL, but the comment before the existing
> > msleep() claims *it* is the T_PVPERL delay:
> > 
> >          * Described in PCIe CEM specification sections 2.2 (PERST#
> > Signal)
> >          * and 2.2.1 (Initial Power-Up (G3 to S0)).
> >          * The deassertion of PERST# should be delayed 100ms
> > (TPVPERL)
> >          * for the power and clock to become stable.
> > 
> > >  	msleep(100);
> > >  
> > >  	/* De-assert reset signals */
> > > -	val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB |
> > > PCIE_PE_RSTB);
> > > +	val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB);
> > > +	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > > +
> > > +	msleep(100);
> > > 
> > 
> > So I'm confused about these two sleeps.  Are they for different
> > parameters?
> > 
> > T_PVPERL is defined from "Power stable to PERST# inactive".  Do we
> > have any actual indication of when to start that delay, i.e., do we
> > have a clue about when power became stable?
> > 
> > > +	/* De-assert PERST# signals */
> > > +	val &= ~(PCIE_PE_RSTB);
> > >  	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > >  
> > >  	/* Check if the link is up or not */
> > > -- 
> > > 2.42.0
> > > linux-arm-kernel mailing list
> > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 
> Hi
> 
> Seems it is same as the patch i've sent some time ago and which was
> rejected because of the additional delay...
> 
> 
https://patchwork.kernel.org/project/linux-mediatek/patch/20230402131347.99268-1-linux@xxxxxxxxx/
> 
> Or am i wrong?
> regards Frank

Hi Daniel,

Did you found this issue on MT7986(BPI-R3) or other platforms?

Can you share the PCIe device model that failed to link up?

Thanks.