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

[Christian Marangi <ansuelsmth@gmail.com>]

On Tue, Oct 10, 2023 at 06:42:07PM +0200, Frank Wunderlich wrote:
> Am 10. Oktober 2023 18:04:23 MESZ schrieb Bjorn Helgaas <helgaas@kernel.org>:
> >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@makrotopia.org>
> >> ---
> >>  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@lists.infradead.org
> >> 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@fw-web.de/
> 
> Or am i wrong?
> regards Frank

Reading the other series, I smell this can only be handled by a quirk...
This might be a defect or the board not following PCIE hw specs.

Thing is that the bug/limitation is there and we have enough info to
find way to fix this and lots of tester.

Eventually even a fixup based on a specific compatible.

-- 
	Ansuel