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

From: Luca Ceresoli <luca@lucaceresoli.net>
To: Marc Zyngier <maz@kernel.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org
Cc: "Pali Rohár" <pali@kernel.org>,
	"Alyssa Rosenzweig" <alyssa@rosenzweig.io>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Mark Kettenis" <mark.kettenis@xs4all.nl>,
	kernel-team@android.com
Subject: Re: [PATCH v3 3/3] PCI: apple: Fix #PERST polarity
Date: Tue, 23 Nov 2021 22:36:11 +0100	[thread overview]
Message-ID: <453389da-b041-94b3-009e-6c6323134936@lucaceresoli.net> (raw)
In-Reply-To: <20211123180636.80558-4-maz@kernel.org>

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@kernel.org>
> Signed-off-by: Marc Zyngier <maz@kernel.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