staging: comedi: adl_pci9118: don't overallocate DMA buffer

The last parameter of `__get_free_pages()` is log2 (the 'order') of the
number of pages to be allocated.  This driver seems to think it is the
linear number of pages, so `pci9118_alloc_dma()` first tries to allocate
16 pages, but only uses 4 of them, setting the buffer size to PAGE_SIZE
multiplied by the 'order'.  If the allocation fails, it tries
progressively smaller orders, down to 0.  If the allocation at order 0
succeeds, the buffer size is set to 0, which is likely to cause
problems.

Set the buffer size to `PAGE_SIZE` shifted left by the allocation order.
Since the maximum buffer size previously used was 4, start with an
allocation order of 2 instead of 4.  Rename the `pages` member of
`struct pci9118_dmabuf` (and the local variable in
`pci9118_alloc_dma()`) to `order` to make it clearer what it is.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/adl_pci9118.c b/drivers/staging/comedi/drivers/adl_pci9118.c
index 116910401067f3ca83f0d1ab9ed14923d812c467..6ab9e0a27588de490a124021c056e11668492e15 100644 (file)
--- a/drivers/staging/comedi/drivers/adl_pci9118.c
+++ b/drivers/staging/comedi/drivers/adl_pci9118.c
@@ -208,7 +208,7 @@ struct pci9118_dmabuf {
        unsigned long hw;       /* hardware (bus) address of buffer */
        unsigned int size;      /* size of dma buffer in bytes */
        unsigned int use_size;  /* which size we may now use for transfer */
-       int pages;              /* number of pages in buffer */
+       int order;              /* log2 number of pages in buffer */
 };
 
 struct pci9118_private {
@@ -1479,20 +1479,20 @@ static void pci9118_alloc_dma(struct comedi_device *dev)
 {
        struct pci9118_private *devpriv = dev->private;
        struct pci9118_dmabuf *dmabuf;
-       int pages;
+       int order;
        int i;
 
        for (i = 0; i < 2; i++) {
                dmabuf = &devpriv->dmabuf[i];
-               for (pages = 4; pages >= 0; pages--) {
-                       dmabuf->virt = __get_free_pages(GFP_KERNEL, pages);
+               for (order = 2; order >= 0; order--) {
+                       dmabuf->virt = __get_free_pages(GFP_KERNEL, order);
                        if (dmabuf->virt)
                                break;
                }
                if (!dmabuf->virt)
                        break;
-               dmabuf->pages = pages;
-               dmabuf->size = PAGE_SIZE * pages;
+               dmabuf->order = order;
+               dmabuf->size = PAGE_SIZE << order;
                dmabuf->hw = virt_to_bus((void *)dmabuf->virt);
 
                if (i == 0)
@@ -1514,7 +1514,7 @@ static void pci9118_free_dma(struct comedi_device *dev)
        for (i = 0; i < 2; i++) {
                dmabuf = &devpriv->dmabuf[i];
                if (dmabuf->virt)
-                       free_pages(dmabuf->virt, dmabuf->pages);
+                       free_pages(dmabuf->virt, dmabuf->order);
        }
 }