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

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Date: Fri, 19 Apr 2024 15:08:47 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.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 11:12:09AM -0500, Bjorn Helgaas wrote:
> 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.
> 

That's my bad. I'll remove it.

> 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?
> 

Yes, the PCIe endpoint controller generates an IRQ when host sets Bus Master
Enable bit.

> > - * 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"?
> 

Yes. But looking at it again, it could be reworded as below:

'Invoke to notify the EPF device that the EPC device has generated the Bus
Master Enable event due to host setting the Bus Master Enable bit in the
Command register.'

- Mani

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