From: Niklas Cassel <cassel@kernel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: "Lorenzo Pieralisi" <lpieralisi@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Rob Herring" <robh@kernel.org>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Heiko Stuebner" <heiko@sntech.de>,
"Damien Le Moal" <dlemoal@kernel.org>,
linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-rockchip@lists.infradead.org
Subject: Re: [PATCH] PCI: dw-rockchip: Fix GPIO initialization flag
Date: Tue, 16 Apr 2024 13:49:27 +0200 [thread overview]
Message-ID: <Zh5lx9r1H6MO3kEs@ryzen> (raw)
In-Reply-To: <20240416112807.GC2454@thinkpad>
On Tue, Apr 16, 2024 at 04:58:07PM +0530, Manivannan Sadhasivam wrote:
> On Wed, Mar 27, 2024 at 04:25:31PM +0100, Niklas Cassel wrote:
> > PERST is active low according to the PCIe specification.
> >
> > However, the existing pcie-dw-rockchip.c driver does:
> > gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1);
> > When asserting + deasserting PERST.
> >
> > This is of course wrong, but because all the device trees for this
> > compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
> > $ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
> > $ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*
> >
> > The actual toggling of PERST is correct.
> > (And we cannot change it anyway, since that would break device tree
> > compatibility.)
> >
> > However, this driver does request the GPIO to be initialized as
> > GPIOD_OUT_HIGH, which does cause a silly sequence where PERST gets
> > toggled back and forth for no good reason.
> >
> > Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW
> > (which for this driver means PERST asserted).
> >
> > This will avoid an unnecessary signal change where PERST gets deasserted
> > (by devm_gpiod_get_optional()) and then gets asserted
> > (by rockchip_pcie_start_link()) just a few instructions later.
> >
> > Before patch, debug prints on EP side, when booting RC:
> > [ 845.606810] pci: PERST asserted by host!
> > [ 852.483985] pci: PERST de-asserted by host!
> > [ 852.503041] pci: PERST asserted by host!
> > [ 852.610318] pci: PERST de-asserted by host!
> >
> > After patch, debug prints on EP side, when booting RC:
> > [ 125.107921] pci: PERST asserted by host!
> > [ 132.111429] pci: PERST de-asserted by host!
> >
> > Without this change, there is no guarantee that PERST will be asserted
> > while the core is performing a fundamental reset.
> There is no 'core' here, are you referring to the device?
If you at pcie-qcom.c, it does:
1) PERST# assert
2) core reset (using reset_control_assert() in ops->init())
3) PERST# deassert
So the EP is held in reset while the RC resets.
Right now, for dw-rockchip driver, there is no guarantee that
EP is held in reset when the core on RC side resets, which seems bad.
>
> > (E.g. if the bootloader would leave PERST deasserted.)
> >
>
> I don't follow this last sentence. But even without that, the commit message
> itself is descriptive enough.
When I flash u-boot on my board, and boot using TFTP,
I can see that when u-boot jumps to Linux, PERST# is not asserted
and will not be asserted when PCIe RC driver loads.
So the scenario mentioned above can happen.
(If I don't boot using TFTP, PERST# is deasserted when PCIe RC driver loads.)
Anyway, I will remove or clarify this sentence.
>
> > Signed-off-by: Niklas Cassel <cassel@kernel.org>
>
> This is a legitimate bug fix. So you should add the fixes tag and CC stable to
> get it backported.
Ok, will do in V2.
>
> But the patch itself looks fine to me.
>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Thank you.
Kind regards,
Niklas
prev parent reply other threads:[~2024-04-16 11:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-27 15:25 [PATCH] PCI: dw-rockchip: Fix GPIO initialization flag Niklas Cassel
2024-04-16 10:35 ` Jianfeng Liu
2024-04-16 11:28 ` Manivannan Sadhasivam
2024-04-16 11:49 ` Niklas Cassel [this message]
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