linux-kernel - [PATCH v2] PCI: endpoint: pci-epf-test: Move DMA check into read/write/copy functions

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Message-Id: <20240819120112.23563-1-rick.wertenbroek@gmail.com>
Date: Mon, 19 Aug 2024 14:01:10 +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 v2] PCI: endpoint: pci-epf-test: Move DMA check into read/write/copy functions

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 inside 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.

Move the DMA check into the pci_epf_test_read()/write()/copy() functions
so that they report a transfer (IO) error and that pci_epf_test_raise_irq()
is called when a transfer with DMA is requested, even if 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.

Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>
---
 drivers/pci/endpoint/functions/pci-epf-test.c | 29 +++++++++++++++----
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index 7c2ed6eae53a..ec0f79383521 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -314,6 +314,17 @@ static void pci_epf_test_print_rate(struct pci_epf_test *epf_test,
 		 (u64)ts.tv_sec, (u32)ts.tv_nsec, rate);
 }
 
+static int pci_epf_test_check_dma(struct pci_epf_test *epf_test,
+				   struct pci_epf_test_reg *reg)
+{
+	if ((READ_ONCE(reg->flags) & FLAG_USE_DMA) &&
+	    !epf_test->dma_supported) {
+		dev_err(&epf_test->epf->dev, "DMA transfer not supported\n");
+		return -EIO;
+	}
+	return 0;
+}
+
 static void pci_epf_test_copy(struct pci_epf_test *epf_test,
 			      struct pci_epf_test_reg *reg)
 {
@@ -327,6 +338,10 @@ static void pci_epf_test_copy(struct pci_epf_test *epf_test,
 	struct device *dev = &epf->dev;
 	struct pci_epc *epc = epf->epc;
 
+	ret = pci_epf_test_check_dma(epf_test, reg);
+	if (ret)
+		goto err;
+
 	src_addr = pci_epc_mem_alloc_addr(epc, &src_phys_addr, reg->size);
 	if (!src_addr) {
 		dev_err(dev, "Failed to allocate source address\n");
@@ -423,6 +438,10 @@ static void pci_epf_test_read(struct pci_epf_test *epf_test,
 	struct pci_epc *epc = epf->epc;
 	struct device *dma_dev = epf->epc->dev.parent;
 
+	ret = pci_epf_test_check_dma(epf_test, reg);
+	if (ret)
+		goto err;
+
 	src_addr = pci_epc_mem_alloc_addr(epc, &phys_addr, reg->size);
 	if (!src_addr) {
 		dev_err(dev, "Failed to allocate address\n");
@@ -507,6 +526,10 @@ static void pci_epf_test_write(struct pci_epf_test *epf_test,
 	struct pci_epc *epc = epf->epc;
 	struct device *dma_dev = epf->epc->dev.parent;
 
+	ret = pci_epf_test_check_dma(epf_test, reg);
+	if (ret)
+		goto err;
+
 	dst_addr = pci_epc_mem_alloc_addr(epc, &phys_addr, reg->size);
 	if (!dst_addr) {
 		dev_err(dev, "Failed to allocate address\n");
@@ -647,12 +670,6 @@ static void pci_epf_test_cmd_handler(struct work_struct *work)
 	WRITE_ONCE(reg->command, 0);
 	WRITE_ONCE(reg->status, 0);
 
-	if ((READ_ONCE(reg->flags) & FLAG_USE_DMA) &&
-	    !epf_test->dma_supported) {
-		dev_err(dev, "Cannot transfer data using DMA\n");
-		goto reset_handler;
-	}
-
 	if (reg->irq_type > IRQ_TYPE_MSIX) {
 		dev_err(dev, "Failed to detect IRQ type\n");
 		goto reset_handler;
-- 
2.25.1