Re: [PATCH] PCI: apple: Reset the port for 100ms on probe

Bjorn Helgaas
2021-11-17T20:12:48Z

[+cc Pali]

On Wed, Nov 17, 2021 at 04:00:53PM +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).

s/beacuse/because/

> Bring the port back to life by wiggling the #PERST pin for 100ms
> (as per the spec).

I cc'd Pali because I think he's interested in consolidating or
somehow rationalizing delays like this.

If we have a specific spec reference here, I think it would help that
effort. I *think* it's PCIe r5.0, sec 6.6.1, which mentions the 100ms
along with some additional constraints, like waiting 100ms after Link
training completes for ports that support > 5.0 GT/s, whether
Readiness Notifications are used, and CRS Software Visiblity.

> Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up")
> 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 | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> index 1bf4d75b61be..bbea5f6e0a68 100644
> --- a/drivers/pci/controller/pcie-apple.c
> +++ b/drivers/pci/controller/pcie-apple.c
> @@ -543,6 +543,9 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie,
> if (ret < 0)
> return ret;
>
> + /* Hold #PERST for 100ms as per the spec */
> + gpiod_set_value(reset, 0);
> + msleep(100);
> rmw_set(PORT_PERST_OFF, port->base + PORT_PERST);
> gpiod_set_value(reset, 1);
>
> --
> 2.30.2
>