Messages in this thread | | | Date | Wed, 24 Nov 2021 12:56:06 +0000 | Subject | Re: [PATCH v3 1/3] PCI: apple: Follow the PCIe specifications when resetting the port | From | Robin Murphy <> |
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On 2021-11-23 18:06, Marc Zyngier wrote: > While the Apple PCIe driver works correctly when directly booted > from the firmware, it fails to initialise when the kernel is booted > from a bootloader using PCIe such as u-boot. > > That's beacuse we're missing a proper reset of the port (we only > clear the reset, but never assert it). > > The PCIe spec requirements are two-fold: > > - #PERST must be asserted before setting up the clocks, and > stay asserted for at least 100us (Tperst-clk). > > - Once #PERST is deasserted, the OS must wait for at least 100ms > "from the end of a Conventional Reset" before we can start talking > to the devices > > Implementing this results in a booting system. > > Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up") > Acked-by: Pali Rohár <pali@kernel.org> > Signed-off-by: Marc Zyngier <maz@kernel.org> > Cc: Alyssa Rosenzweig <alyssa@rosenzweig.io> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> > Cc: Bjorn Helgaas <bhelgaas@google.com> > --- > drivers/pci/controller/pcie-apple.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c > index 1bf4d75b61be..957960a733c4 100644 > --- a/drivers/pci/controller/pcie-apple.c > +++ b/drivers/pci/controller/pcie-apple.c > @@ -539,13 +539,23 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie, > > rmw_set(PORT_APPCLK_EN, port->base + PORT_APPCLK); > > + /* Engage #PERST before setting up the clock */ > + gpiod_set_value(reset, 0);
FWIW, given that getting the GPIO with GPIOD_OUT_LOW should have had this effect in the first place, if this isn't a no-op at this point then it would hint at something being more significantly wrong down at the GPIO/pinctrl end :/
Once you fix the polarity in the later patch, though, adding the explicit reset assertion here does seem a far nicer option than fiddling the flags to preserve the implicit assertion earlier.
Cheers, Robin.
> + > ret = apple_pcie_setup_refclk(pcie, port); > if (ret < 0) > return ret; > > + /* The minimal Tperst-clk value is 100us (PCIe CMS r2.0, 2.6.2) */ > + usleep_range(100, 200); > + > + /* Deassert #PERST */ > rmw_set(PORT_PERST_OFF, port->base + PORT_PERST); > gpiod_set_value(reset, 1); > > + /* Wait for 100ms after #PERST deassertion (PCIe r2.0, 6.6.1) */ > + msleep(100); > + > ret = readl_relaxed_poll_timeout(port->base + PORT_STATUS, stat, > stat & PORT_STATUS_READY, 100, 250000); > if (ret < 0) { >
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