linux-kernel - Re: [PATCH v5 -next 07/11] PCI: brcmstb: Adjust PHY PLL setup to use a 54MHz input refclk

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Message-ID: <e6dc990a-81bb-4185-848e-4202aa7bb839@suse.de>
Date: Sun, 23 Feb 2025 11:50:48 +0200
From: Stanimir Varbanov <svarbanov@...e.de>
To: Bjorn Helgaas <helgaas@...nel.org>, Stanimir Varbanov <svarbanov@...e.de>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rpi-kernel@...ts.infradead.org,
 linux-pci@...r.kernel.org,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Thomas Gleixner
 <tglx@...utronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Florian Fainelli <florian.fainelli@...adcom.com>,
 Jim Quinlan <jim2101024@...il.com>,
 Nicolas Saenz Julienne <nsaenz@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, kw@...ux.com,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Andrea della Porta <andrea.porta@...e.com>,
 Phil Elwell <phil@...pberrypi.com>, Jonathan Bell
 <jonathan@...pberrypi.com>, Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: Re: [PATCH v5 -next 07/11] PCI: brcmstb: Adjust PHY PLL setup to use
 a 54MHz input refclk

Hi Bjorn,

On 2/21/25 11:33 PM, Bjorn Helgaas wrote:
> On Mon, Jan 20, 2025 at 03:01:15PM +0200, Stanimir Varbanov wrote:
>> The default input reference clock for the PHY PLL is 100Mhz, except for
>> some devices where it is 54Mhz like bcm2712C1 and bcm2712D0.
>>
>> To implement this adjustments introduce a new .post_setup op in
>> pcie_cfg_data and call it at the end of brcm_pcie_setup function.
>>
>> The bcm2712 .post_setup callback implements the required MDIO writes that
>> switch the PLL refclk and also change PHY PM clock period.
>>
>> Without this RPi5 PCIex1 is unable to enumerate endpoint devices on
>> the expansion connector.
> 
> This makes it sound like this patch should be reordered before "[PATCH
> v5 -next 06/11] PCI: brcmstb: Add bcm2712 support".
> 
> We don't really want a driver to claim a bcm2712 controller before
> it's able to enumerate devices, because that would break bisection
> through this.

I absolutely agree with you in regards to bisect-ability. But to satisfy
this I have to squash "Adjust PHY PLL ..." into "PCI: brcmstb: Add
bcm2712 support" to avoid a warning about not used function. If that
works I'll send a new rebased controller/brcmstb version (v6).

~Stan