Re: [PATCH v3 1/3] PCI: apple: Follow the PCIe specifications when resetting the port
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2021-12-07 16:23:05
Also in:
linux-pci, lkml
On Tue, Nov 23, 2021 at 06:06:34PM +0000, 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
Unless somebody objects, I'll s/#PERST/PERST#/ to match the spec usage, both here and in the comments below. I also notice gpiod_get_from_of_node(..., "#PERST") earlier in apple_pcie_setup_port(). If it wouldn't break anything, I'd like to change that, too.
quoted hunk ↗ jump to hunk
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 <redacted> Cc: Lorenzo Pieralisi <redacted> 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); + 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);
Spec says "min 100us from REFCLK stable before PERST# inactive". So I guess when apple_pcie_setup_refclk() returns, we know REFCLK is already stable?
+ /* 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);
Does this port support speeds greater than 5 GT/s? If so, 6.6.1 says we need "100ms after Link training completes," not just after deasserting PERST#. I'll update this citation to "PCIe r5.0, 6.6.1" to reference the current spec.
ret = readl_relaxed_poll_timeout(port->base + PORT_STATUS, stat,
stat & PORT_STATUS_READY, 100, 250000);
if (ret < 0) {
--
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