Re: [PATCH] staging: comedi: s626: Remove pci-dma-compat wrapper APIs.

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On 11/07/2020 14:38, Christophe JAILLET wrote:
Le 11/07/2020 à 14:35, Suraj Upadhyay a écrit :
The legacy API wrappers in include/linux/pci-dma-compat.h
should go away as it creates unnecessary midlayering
for include/linux/dma-mapping.h APIs, instead use dma-mapping.h
APIs directly.

The patch has been generated with the coccinelle script below
and compile-tested.

[...]
@@ expression E1, E2, E3; @@
- pci_alloc_consistent(E1, E2, E3)
+ dma_alloc_coherent(&E1->dev, E2, E3, GFP_ATOMIC)

@@ expression E1, E2, E3; @@
- pci_zalloc_consistent(E1, E2, E3)
+ dma_alloc_coherent(&E1->dev, E2, E3, GFP_ATOMIC)

This is the tricky part of this kind of cleanup, see below.

GFP_ATOMIC can't be wrong because it is was exactly what was done with the pci_ function. However, most of the time, it can safely be replaced by GFP_KERNEL which gives more opportunities to the memory allocator.

[...]
diff --git a/drivers/staging/comedi/drivers/s626.c b/drivers/staging/comedi/drivers/s626.c
index 084a8e7b9fc2..c159416662fd 100644
--- a/drivers/staging/comedi/drivers/s626.c
+++ b/drivers/staging/comedi/drivers/s626.c
@@ -2130,13 +2130,15 @@ static int s626_allocate_dma_buffers(struct comedi_device *dev)
      void *addr;
      dma_addr_t appdma;
-    addr = pci_alloc_consistent(pcidev, S626_DMABUF_SIZE, &appdma);
+    addr = dma_alloc_coherent(&pcidev->dev, S626_DMABUF_SIZE, &appdma,
+                  GFP_ATOMIC);
      if (!addr)
          return -ENOMEM;
      devpriv->ana_buf.logical_base = addr;
      devpriv->ana_buf.physical_base = appdma;
-    addr = pci_alloc_consistent(pcidev, S626_DMABUF_SIZE, &appdma);
+    addr = dma_alloc_coherent(&pcidev->dev, S626_DMABUF_SIZE, &appdma,
+                  GFP_ATOMIC);
      if (!addr)
          return -ENOMEM;
      devpriv->rps_buf.logical_base = addr;
's626_allocate_dma_buffers()' is only called from 's626_auto_attach()'.
In this function, around the call to 's626_allocate_dma_buffers()', you can see:
   - a few lines before, a call to 'comedi_alloc_devpriv()'

   - a few lines after, a call to 'comedi_alloc_subdevices()'

These 2 functions make some memory allocation using GFP_KERNEL.

So it is likely that using GFP_KERNEL in your proposal is also valid.

Indeed, GFP_KERNEL is perfectly fine here. It could be done as a follow-up patch, or done in a v2 of this patch with a mention in the patch description.

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