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

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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>
This commit is contained in:
Ian Abbott 2014-09-12 10:04:43 +01:00 • committed by Greg Kroah-Hartman
parent d5733baf23
commit f39f87e9ea
1 changed files with 7 additions and 7 deletions
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14
drivers/staging/comedi/drivers/adl_pci9118.c
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@ -208,7 +208,7 @@ struct pci9118_dmabuf {
unsigned long hw; /* hardware (bus) address of buffer */ unsigned long hw; /* hardware (bus) address of buffer */
unsigned int size; /* size of dma buffer in bytes */ unsigned int size; /* size of dma buffer in bytes */
unsigned int use_size; /* which size we may now use for transfer */ 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 { struct pci9118_private {
@ -1479,20 +1479,20 @@ static void pci9118_alloc_dma(struct comedi_device *dev)
{ {
struct pci9118_private *devpriv = dev->private; struct pci9118_private *devpriv = dev->private;
struct pci9118_dmabuf *dmabuf; struct pci9118_dmabuf *dmabuf;
int pages; int order;
int i; int i;
for (i = 0; i < 2; i++) { for (i = 0; i < 2; i++) {
dmabuf = &devpriv->dmabuf[i]; dmabuf = &devpriv->dmabuf[i];
for (pages = 4; pages >= 0; pages--) { for (order = 2; order >= 0; order--) {
dmabuf->virt = __get_free_pages(GFP_KERNEL, pages); dmabuf->virt = __get_free_pages(GFP_KERNEL, order);
if (dmabuf->virt) if (dmabuf->virt)
break; break;
} }
if (!dmabuf->virt) if (!dmabuf->virt)
break; break;
dmabuf->pages = pages; dmabuf->order = order;
dmabuf->size = PAGE_SIZE * pages; dmabuf->size = PAGE_SIZE << order;
dmabuf->hw = virt_to_bus((void *)dmabuf->virt); dmabuf->hw = virt_to_bus((void *)dmabuf->virt);
if (i == 0) if (i == 0)
@ -1514,7 +1514,7 @@ static void pci9118_free_dma(struct comedi_device *dev)
for (i = 0; i < 2; i++) { for (i = 0; i < 2; i++) {
dmabuf = &devpriv->dmabuf[i]; dmabuf = &devpriv->dmabuf[i];
if (dmabuf->virt) if (dmabuf->virt)
free_pages(dmabuf->virt, dmabuf->pages); free_pages(dmabuf->virt, dmabuf->order);
} }
} }