linux-kernel - [PATCH] PCI: endpoint: functions/pci-epf-test: Enable picking DMA channel by name

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Date:   Fri,  1 May 2020 09:20:08 -0700
From:   Alan Mikhak <alan.mikhak@...ive.com>
To:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kishon@...com, lorenzo.pieralisi@....com, bhelgaas@...gle.com,
        ulf.hansson@...aro.org, sebott@...ux.ibm.com, efremov@...ux.com,
        vidyas@...dia.com, paul.walmsley@...ive.com
Cc:     Alan Mikhak <alan.mikhak@...ive.com>
Subject: [PATCH] PCI: endpoint: functions/pci-epf-test: Enable picking DMA channel by name

From: Alan Mikhak <alan.mikhak@...ive.com>

Modify pci_epf_test_init_dma_chan() to call dma_request_channel() with a
filter function to pick DMA channel by name, if desired.

Add a new filter function pci_epf_test_pick_dma_chan() which takes a name
string as an optional parameter. If desired name is specified, the filter
function checks the name of each DMA channel candidate against the desired
name. If no match, the filter function rejects the candidate channel.
Otherwise, the candidate channel is accepted. If optional name parameter
is null or an empty string, filter function picks the first DMA channel
candidate, thereby preserving the existing behavior of pci-epf-test.

Currently, pci-epf-test picks the first suitable DMA channel. Adding a
filter function enables a developer to modify the optional parameter
during debugging by providing the name of a desired DMA channel. This is
useful during debugging because it allows different DMA channels to be
exercised.

Adding a filter function also takes one step toward modifying pcitest to
allow the user to choose a DMA channel by providing a name string at the
command line when issuing the -d parameter for DMA transfers.

Signed-off-by: Alan Mikhak <alan.mikhak@...ive.com>
---
 drivers/pci/endpoint/functions/pci-epf-test.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index 60330f3e3751..043916d3ab5f 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -149,10 +149,26 @@ static int pci_epf_test_data_transfer(struct pci_epf_test *epf_test,
 }

 /**
- * pci_epf_test_init_dma_chan() - Function to initialize EPF test DMA channel
- * @epf_test: the EPF test device that performs data transfer operation
+ * pci_epf_test_pick_dma_chan() - Filter DMA channel based on desired criteria
+ * @chan: the DMA channel to examine
  *
- * Function to initialize EPF test DMA channel.
+ * Filter DMA channel candidates by matching against an optional desired name.
+ * Pick first candidate channel if desired name is not specified.
+ * Reject candidate channel if its name does not match the desired name.
+ */
+static bool pci_epf_test_pick_dma_chan(struct dma_chan *chan, void *name)
+{
+	if (name && strlen(name) && strcmp(dma_chan_name(chan), name))
+		return false;
+
+	return true;
+}
+
+/**
+ * pci_epf_test_init_dma_chan() - Helper to initialize EPF DMA channel
+ * @epf: the EPF device that has to perform the data transfer operation
+ *
+ * Helper to initialize EPF DMA channel.
  */
 static int pci_epf_test_init_dma_chan(struct pci_epf_test *epf_test)
 {
@@ -165,7 +181,7 @@ static int pci_epf_test_init_dma_chan(struct pci_epf_test *epf_test)
 	dma_cap_zero(mask);
 	dma_cap_set(DMA_MEMCPY, mask);

-	dma_chan = dma_request_chan_by_mask(&mask);
+	dma_chan = dma_request_channel(mask, pci_epf_test_pick_dma_chan, NULL);
 	if (IS_ERR(dma_chan)) {
 		ret = PTR_ERR(dma_chan);
 		if (ret != -EPROBE_DEFER)
-- 
2.7.4