linux-kernel - Re: [PATCH v3 3/9] PCI: endpoint: Rename BME to Bus Master Enable

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Date: Thu, 18 Apr 2024 11:12:09 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Jingoo Han <jingoohan1@...il.com>, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	mhi@...ts.linux.dev, linux-tegra@...r.kernel.org,
	Niklas Cassel <cassel@...nel.org>,
	Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [PATCH v3 3/9] PCI: endpoint: Rename BME to Bus Master Enable

On Thu, Apr 18, 2024 at 05:28:31PM +0530, Manivannan Sadhasivam wrote:
> BME which stands for 'Bus Master Enable' is not defined in the PCIe base
> spec even though it is commonly referred in many places (vendor docs). But
> to align with the spec, let's rename it to its expansion 'Bus Master
> Enable'.

Thanks for doing this.  I'm always in favor of using terms from the
spec.

> -		dev_dbg(dev, "Received BME event. Link is enabled!\n");
> +		dev_dbg(dev, "Received Bus Master Enable event. Link is enabled!\n");

Nothing to do with *this* patch, but this message reads a little weird
to me because setting Bus Master Enable has nothing to do with link
enablement.

Also incidental: some of these messages and comments refer to a "Bus
Master Enable *event*".  Does "event" here refer to the act of the
host setting the Bus Master Enable bit in the Command register?  This
is in qcom_pcie_ep_global_irq_thread(), so I assume there's something
in the endpoint hardware that generates an IRQ when the Command
register is written?

> - * pci_epc_bme_notify() - Notify the EPF device that the EPC device has received
> - *			  the BME event from the Root complex
> - * @epc: the EPC device that received the BME event
> + * pci_epc_bus_master_enable_notify() - Notify the EPF device that the EPC
> + *					device has received the Bus Master
> + *					Enable event from the Root complex
> + * @epc: the EPC device that received the Bus Master Enable event
>   *
>   * Invoke to Notify the EPF device that the EPC device has received the Bus
> - * Master Enable (BME) event from the Root complex
> + * Master Enable event from the Root complex

There's no "set Bus Master Enable" transaction that would appear on
the PCIe link, so I assume "the Bus Master Enable event from the Root
Complex" is a way of saying something like "host has written the
Command register to set the Bus Master Enable bit"?

Bjorn