linux-kernel - Re: [PATCH linu-next v1] PCI: dw-rockchip: Enable async probe by default

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Message-ID: <20240807170011.GC5664@thinkpad>
Date: Wed, 7 Aug 2024 22:30:11 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Anand Moon <linux.amoon@...il.com>,
	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 linu-next v1] PCI: dw-rockchip: Enable async probe by
 default

On Wed, Aug 07, 2024 at 11:31:06AM -0500, Bjorn Helgaas wrote:
> On Tue, Jun 25, 2024 at 09:27:57PM +0530, Anand Moon wrote:
> > Rockchip PCIe driver lets waits for the combo PHY link like PCIe 3.0,
> > PCIe 2.0 and SATA 3.0 controller to be up during the probe this
> > consumes several milliseconds during boot.
> 
> This needs some wordsmithing.  "driver lets waits" ... I guess "lets"
> is not supposed to be there?  I'm not sure what the relevance of "PCIe
> 3.0, PCIe 2.0, SATA 3.0" is.  I assume the host controller driver
> doesn't know what downstream devices might be present, and the async
> probing is desirable no matter what they might be?
> 

Since the DWC driver is enabling link training during boot, it also waits for
the link to be 'up'. But if the device is 'up', then the wait time would be
usually negligible (few ms). But if there is no device, then the wait time of 1s
would be evident.

But here the patch is trying to avoid the few ms delay itself (which is fine).
The type of endpoint might have some impact on the link training also. But async
probe is always preferred.

- Mani

> > Establishing a PCIe link can take a while; allow asynchronous probing so
> > that link establishment can happen in the background while other devices
> > are being probed.
> > 
> > Signed-off-by: Anand Moon <linux.amoon@...il.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-dw-rockchip.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> > index 61b1acba7182..74a3e9d172a0 100644
> > --- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> > +++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> > @@ -367,6 +367,7 @@ static struct platform_driver rockchip_pcie_driver = {
> >  		.name	= "rockchip-dw-pcie",
> >  		.of_match_table = rockchip_pcie_of_match,
> >  		.suppress_bind_attrs = true,
> > +		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
> >  	},
> >  	.probe = rockchip_pcie_probe,
> >  };
> > -- 
> > 2.44.0
> > 
> 

-- 
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