linux-kernel - Re: [PATCH v8 4/6] PCI: endpoint: pci-epf-test: Add doorbell test support

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Message-ID: <Z0beIUiqXsz5DwVJ@ryzen>
Date: Wed, 27 Nov 2024 09:53:53 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	imx@...ts.linux.dev, dlemoal@...nel.org, maz@...nel.org,
	tglx@...utronix.de, jdmason@...zu.us
Subject: Re: [PATCH v8 4/6] PCI: endpoint: pci-epf-test: Add doorbell test
 support

On Tue, Nov 26, 2024 at 11:55:13AM -0500, Frank Li wrote:
> On Tue, Nov 26, 2024 at 06:11:12PM +0530, Manivannan Sadhasivam wrote:
> > On Tue, Nov 26, 2024 at 11:00:09AM +0100, Niklas Cassel wrote:
> > > On Tue, Nov 26, 2024 at 09:55:23AM +0530, Manivannan Sadhasivam wrote:
> > > > On Mon, Nov 25, 2024 at 02:17:04PM -0500, Frank Li wrote:
> > > > > On Sun, Nov 24, 2024 at 01:26:45PM +0530, Manivannan Sadhasivam wrote:
> > > > > > On Sat, Nov 16, 2024 at 09:40:44AM -0500, Frank Li wrote:
> > > > > > > Add three registers: doorbell_bar, doorbell_addr, and doorbell_data,
> >
> > I like the idea of calling pci_epf_alloc_doorbell() in
> > pci_epf_{enable/disable}_doorbell() APIs. And as you said, it doesn't make sense
> > to call these APIs too frequently.
> 
> I not sure what's you means and direction for next version.

Move pci_epf_alloc_doorbell() from .bind() to pci_epf_enable_doorbell().
Move pci_epf_free_doorbell() from .unbind() to pci_epf_disable_doorbell().

If the pci_epf_alloc_doorbell() call within pci_epf_enable_doorbell() fails,
let pci_epf_enable_doorbell() set STATUS_DOORBELL_ENABLE_FAIL.


> This patch just go first step. If we can append to ITS to bar0 in future,
> pci_epf_alloc_doorbell() will become more reasonable at bind() function.

To be fair, we are probably quite far away from supporting a BAR with two
backing memory areas. It would require a lot of changes in the PCI endpoint
framework, and a lot of changes in the DWC driver.

And even if we do add all the support for it, why can't we keep the
doorbell allocation in pci_epf_enable_doorbell() ?


Kind regards,
Niklas