Re: [PATCH v3 1/3] PCI: apple: Follow the PCIe specifications when resetting the port

Luca Ceresoli
2021-11-24T09:22:30Z

Hi,

On 23/11/21 19:06, 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 */

"Assert" is the verb typically used instead of "Engage".

With this fixed, or even without as this is a pretty urgent fix:

Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>

--
Luca