linux-kernel - [PATCH v3 1/1] PCI: endpoint: pci-epf-test: Call pci_epf_test_raise

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Message-Id: <20240820071100.211622-2-rick.wertenbroek@gmail.com>
Date: Tue, 20 Aug 2024 09:10:58 +0200
From: Rick Wertenbroek <rick.wertenbroek@...il.com>
To: rick.wertenbroek@...g-vd.ch
Cc: dlemoal@...nel.org,
	alberto.dassatti@...g-vd.ch,
	Rick Wertenbroek <rick.wertenbroek@...il.com>,
	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: [PATCH v3 1/1] PCI: endpoint: pci-epf-test: Call pci_epf_test_raise_irq() on failed DMA check

The pci-epf-test PCI endpoint function /drivers/pci/endpoint/function/pci-epf_test.c
is meant to be used in a PCI endpoint device connected to a host computer
with the host side driver: /drivers/misc/pci_endpoint_test.c.

The host side driver can request read/write/copy transactions from the
endpoint function and expects an IRQ from the endpoint function once
the read/write/copy transaction is finished. These can be issued with or
without DMA enabled. If the host side driver requests a read/write/copy
transaction with DMA enabled and the endpoint function does not support
DMA, the endpoint would only print an error message and wait for further
commands without sending an IRQ because pci_epf_test_raise_irq() is
skipped in pci_epf_test_cmd_handler(). This results in the host side
driver hanging indefinitely waiting for the IRQ.

Call pci_epf_test_raise_irq() when a transfer with DMA is requested but
DMA is unsupported. The host side driver will no longer hang but report
an error on transfer (printing "NOT OKAY") thanks to the checksum because
no data was moved.

Clarify the error message in the endpoint function as "Cannot ..." is
vague and does not state the reason why it cannot be done.

Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>
---
 drivers/pci/endpoint/functions/pci-epf-test.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index 7c2ed6eae53a..b02193cef06e 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -649,7 +649,8 @@ static void pci_epf_test_cmd_handler(struct work_struct *work)

 	if ((READ_ONCE(reg->flags) & FLAG_USE_DMA) &&
 	    !epf_test->dma_supported) {
-		dev_err(dev, "Cannot transfer data using DMA\n");
+		dev_err(dev, "DMA transfer not supported\n");
+		pci_epf_test_raise_irq(epf_test, reg);
 		goto reset_handler;
 	}

-- 
2.25.1