[v2,1/1] misc: pci_endpoint_test: Refactor dma_set_mask_and_coherent() logic

Commit Message

Frank Li May 2, 2024, 7:59 p.m. UTC

dma_set_mask_and_coherent() should never fail when the mask is >= 32bit,
unless the architecture has no DMA support. So no need check for the error
and also no need to set dma_set_mask_and_coherent(32) as a fallback.

Even if dma_set_mask_and_coherent(48) fails due to the lack of DMA support
(theoretically), then dma_set_mask_and_coherent(32) will also fail for the
same reason. So the fallback doesn't make sense.

Due to the above reasons, let's simplify the code by setting the streaming
and coherent DMA mask to 48 bits.

Reviewed-by: Manivannan Sadhasivam <[e-mail]>
Signed-off-by: Frank Li <[e-mail]>
---

Notes:
    Change from v1 to v2:
    - Rework commit message according to mani's feedback.
    - Not sure why set to 48bit at original patch.
    
    Ref: https://lore.kernel.org/linux-pci/[e-mail]/T/#u
    
    for document change patch. DMA document sample code is miss leading.
    fixed patch already accepted:
    https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=f7ae20f2fc4e6a5e32f43c4fa2acab3281a61c81

 drivers/misc/pci_endpoint_test.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Comments

Niklas Cassel May 7, 2024, 7:48 a.m. UTC | #1

On Thu, May 02, 2024 at 03:59:03PM -0400, Frank Li wrote:
> dma_set_mask_and_coherent() should never fail when the mask is >= 32bit,
> unless the architecture has no DMA support. So no need check for the error
> and also no need to set dma_set_mask_and_coherent(32) as a fallback.
> 
> Even if dma_set_mask_and_coherent(48) fails due to the lack of DMA support
> (theoretically), then dma_set_mask_and_coherent(32) will also fail for the
> same reason. So the fallback doesn't make sense.
> 
> Due to the above reasons, let's simplify the code by setting the streaming
> and coherent DMA mask to 48 bits.
> 
> Reviewed-by: Manivannan Sadhasivam <[e-mail]>
> Signed-off-by: Frank Li <[e-mail]>
> ---

Reviewed-by: Niklas Cassel <[e-mail]>

Krzysztof Wilczyński May 17, 2024, 10:03 a.m. UTC | #2

Hello,

> dma_set_mask_and_coherent() should never fail when the mask is >= 32bit,
> unless the architecture has no DMA support. So no need check for the error
> and also no need to set dma_set_mask_and_coherent(32) as a fallback.
> 
> Even if dma_set_mask_and_coherent(48) fails due to the lack of DMA support
> (theoretically), then dma_set_mask_and_coherent(32) will also fail for the
> same reason. So the fallback doesn't make sense.
> 
> Due to the above reasons, let's simplify the code by setting the streaming
> and coherent DMA mask to 48 bits.

Applied to misc, thank you!

[1/1] misc: pci_endpoint_test: Refactor dma_set_mask_and_coherent() logic
      https://git.kernel.org/pci/pci/c/27ea748a3abd

	Krzysztof

Patch

diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
index c38a6083f0a73..56ac6969a8f59 100644
--- a/drivers/misc/pci_endpoint_test.c
+++ b/drivers/misc/pci_endpoint_test.c
@@ -824,11 +824,7 @@  static int pci_endpoint_test_probe(struct pci_dev *pdev,
 	init_completion(&test->irq_raised);
 	mutex_init(&test->mutex);
 
-	if ((dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(48)) != 0) &&
-	    dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)) != 0) {
-		dev_err(dev, "Cannot set DMA mask\n");
-		return -EINVAL;
-	}
+	dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(48));
 
 	err = pci_enable_device(pdev);
 	if (err) {