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

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Message-ID: <60f24740-156e-f679-e77b-3c60ced5b41b@lucaceresoli.net>
Date:   Wed, 24 Nov 2021 10:22:27 +0100
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Marc Zyngier <maz@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org
Cc:     Pali Rohár <pali@...nel.org>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 1/3] PCI: apple: Follow the PCIe specifications when
 resetting the port

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@...nel.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Cc: Alyssa Rosenzweig <alyssa@...enzweig.io>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.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@...aceresoli.net>

-- 
Luca