linux-kernel - Re: [PATCH] PCI: endpoint: pci-epf-test: Move DMA check into read/write/copy functions

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Message-ID: <20240806191541.GA73196@bhelgaas>
Date: Tue, 6 Aug 2024 14:15:41 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Rick Wertenbroek <rick.wertenbroek@...il.com>
Cc: rick.wertenbroek@...g-vd.ch, dlemoal@...nel.org,
	alberto.dassatti@...g-vd.ch,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Niklas Cassel <cassel@...nel.org>, Frank Li <Frank.Li@....com>,
	Lars-Peter Clausen <lars@...afoo.de>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: endpoint: pci-epf-test: Move DMA check into
 read/write/copy functions

On Tue, Aug 06, 2024 at 06:27:54PM +0200, Rick Wertenbroek wrote:
> The test for a DMA transfer was done in pci_epf_test_cmd_handler, which
> if not supported would lead to the endpoint function just printing an
> error message and waiting for further commands. This would leave the

I guess it's the *test* that prints the error message?  Is this the
"Cannot transfer data using DMA" message?

> host side PCI driver waiting for an interrupt because the call to
> pci_epf_test_raise_irq is skipped. The host side driver
> drivers/misc/pci_endpoint_test.c would hang indefinitely when sending
> a transfer request with DMA if the endpoint does not support it.
> This is because wait_for_completion() is used in the host side driver.
> 
> Move the DMA check into the read/write/copy functions so that they
> report a transfer (IO) error so that pci_epf_test_raise_irq() is
> called when a transfer with DMA is requested, even if unsupported.

Add "()" after function names above, as you did for
pci_epf_test_raise_irq().

> The host side driver will still report an error on transfer thanks
> to the checksum, because no data was moved, but will not hang anymore
> waiting for an interrupt that will never arrive.