linux-kernel - Re: [PATCH v3 3/3] PCI: apple: Fix #PERST polarity

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Date:   Tue, 23 Nov 2021 22:36:11 +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 3/3] PCI: apple: Fix #PERST polarity

Hi Mark,

On 23/11/21 19:06, Marc Zyngier wrote:
> Now that #PERST is properly defined as active-low in the device tree,
> fix the driver to correctly drive the line indemendently of the
> implied polarity.
> 
> Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up")
> Suggested-by: Pali Rohár <pali@...nel.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>

Thanks for quickly addressing this!

Do we need a transition path for backward compatibility with old DTs
already around? Something like this [0]. You said [1] the DT actually
used is not even the one in the kernel, thus how do we guarantee DT and
driver switch to the new polarity all at once?

[0] https://lkml.org/lkml/2021/6/24/1049
[1] https://lkml.org/lkml/2021/11/23/455

> ---
>  drivers/pci/controller/pcie-apple.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> index 957960a733c4..03bc56f39be5 100644
> --- a/drivers/pci/controller/pcie-apple.c
> +++ b/drivers/pci/controller/pcie-apple.c
> @@ -540,7 +540,7 @@ 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);
> +	gpiod_set_value(reset, 1);
>  
>  	ret = apple_pcie_setup_refclk(pcie, port);
>  	if (ret < 0)
> @@ -551,7 +551,7 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie,
>  
>  	/* Deassert #PERST */
>  	rmw_set(PORT_PERST_OFF, port->base + PORT_PERST);
> -	gpiod_set_value(reset, 1);
> +	gpiod_set_value(reset, 0);

Minor note: if it were me I would coalesce patches 1 and 3 together,
otherwise we are insisting on a wrong implementation (patch 1) to later
fix it all (this patch).

-- 
Luca