Re: [PATCH v2] PCI: apple: Follow the PCIe specifications when resetting the port
From: Pali Rohár <pali@kernel.org>
Date: 2021-11-22 12:03:53
Also in:
linux-pci, lkml
On Monday 22 November 2021 10:41:56 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")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Alyssa Rosenzweig <redacted>
Cc: Lorenzo Pieralisi <redacted>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Pali Rohár <pali@kernel.org>Looks good, but see comment below. Acked-by: Pali Rohár <pali@kernel.org>
quoted hunk ↗ jump to hunk
--- 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); + + /* Deassert #PERST */ rmw_set(PORT_PERST_OFF, port->base + PORT_PERST); gpiod_set_value(reset, 1);
+ Luca Just one comment. PERST# (PCIe Reset) is active-low signal. De-asserting means to really set value to 1. But there was a discussion that de-asserting should be done by call: gpiod_set_value(reset, 0); https://lore.kernel.org/linux-pci/51be082a-ff10-8a19-5648-f279aabcac51@lucaceresoli.net/ (local) Could we make this new pcie-apple.c driver to use gpiod_set_value(reset, 0) for de-asserting, like in other drivers?
+ /* 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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