linux-kernel - Re: [PATCH v2] PCI: dw-rockchip: Enable async probe by default

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Message-ID: <CANAwSgQEb7rWFaeEO3Mb8LAwK6A5mrCyQFEysmSpeVdhoRWrtw@mail.gmail.com>
Date: Fri, 3 Jan 2025 20:59:51 +0530
From: Anand Moon <linux.amoon@...il.com>
To: Niklas Cassel <cassel@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, Heiko Stuebner <heiko@...ech.de>, 
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: dw-rockchip: Enable async probe by default

Hi Niklas

On Fri, 3 Jan 2025 at 20:40, Niklas Cassel <cassel@...nel.org> wrote:
>
> On Fri, Jan 03, 2025 at 08:36:18PM +0530, Anand Moon wrote:
> > > >
> > > > We need to enable the GMAC PHY and reset it using the proper GPIO pin
> > > > (PCIE_PERST_L).
> > > > Please refer to the schematic for more details.
> > >
> > > The PERST# GPIO is already asserted + deasserted from the PCIe Root Complex
> > > (host) driver:
> > > https://github.com/torvalds/linux/blob/v6.13-rc5/drivers/pci/controller/dwc/pcie-dw-rockchip.c#L191-L206
> > >
> > > which will cause the endpoint device (a RTL8125 NIC in this case)
> > > to be reset during bootup.
> > >
> > Thanks for letting me know. It seems like a workaround.
> > I'll try to disable this and test it again.
> >
> > My point is that we haven't enabled the GMAC PHY (device nodes)
> > and must properly reset the GMAC.
> >
> > We're relying on the code above hack to do that job.
>
> I do not think it is a hack.
>
> If you look in most PCIe controller drivers, they toggle PERST before
> enumerating the bus:
> $ git grep gpiod_set_value drivers/pci/controller/
>

Ok, understood. However, we have multiple reset lines per controller,
so the PCIe driver will reset these lines using gpiod_set_value.

PCIE30X4_PERSTn_M1_L
PCIE30x1_0_PERSTn_M1_L
PCIE_PERST_L
>
> Kind regards,
> Niklas

Thanks
-Anand