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SubjectRe: [PATCH v2] USB: host: Use zeroing memory allocator rather than allocator/memset
On Sun, 31 Dec 2017, Himanshu Jha wrote:

> Use dma_zalloc_coherent for allocating zeroed
> memory and remove unnecessary memset function.
>
> Done using Coccinelle.
> Generated-by: scripts/coccinelle/api/alloc/kzalloc-simple.cocci
> 0-day tested with no failures.
>
> Suggested-by: Luis R. Rodriguez <mcgrof@kernel.org>
> Signed-off-by: Himanshu Jha <himanshujha199640@gmail.com>
> ---
> v2:
> -align argumenst as they were before applying the SmPL rule.

For the UHCI portion:

Acked-by: Alan Stern <stern@rowland.harvard.edu>

But there is something pecular about the patch...

> drivers/usb/host/uhci-hcd.c | 7 +++----
> drivers/usb/host/xhci-mem.c | 7 ++-----
> 2 files changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/usb/host/uhci-hcd.c b/drivers/usb/host/uhci-hcd.c
> index f5c9021..ac53398 100644
> --- a/drivers/usb/host/uhci-hcd.c
> +++ b/drivers/usb/host/uhci-hcd.c
> @@ -600,15 +600,14 @@ static int uhci_start(struct usb_hcd *hcd)
> uhci->dentry = dentry;
> #endif
>
> - uhci->frame = dma_alloc_coherent(uhci_dev(uhci),
> - UHCI_NUMFRAMES * sizeof(*uhci->frame),
> - &uhci->frame_dma_handle, GFP_KERNEL);
> + uhci->frame = dma_zalloc_coherent(uhci_dev(uhci),
> + UHCI_NUMFRAMES * sizeof(*uhci->frame),
> + &uhci->frame_dma_handle, GFP_KERNEL);

The second and third "changed" lines here actually are identical. What
program would produce a diff file showing that they were changed?

Alan Stern

> if (!uhci->frame) {
> dev_err(uhci_dev(uhci),
> "unable to allocate consistent memory for frame list\n");
> goto err_alloc_frame;
> }
> - memset(uhci->frame, 0, UHCI_NUMFRAMES * sizeof(*uhci->frame));
>
> uhci->frame_cpu = kcalloc(UHCI_NUMFRAMES, sizeof(*uhci->frame_cpu),
> GFP_KERNEL);
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 554a8a5..332420d 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -1782,14 +1782,11 @@ int xhci_alloc_erst(struct xhci_hcd *xhci,
> struct xhci_erst_entry *entry;
>
> size = sizeof(struct xhci_erst_entry) * evt_ring->num_segs;
> - erst->entries = dma_alloc_coherent(xhci_to_hcd(xhci)->self.sysdev,
> - size,
> - &erst->erst_dma_addr,
> - flags);
> + erst->entries = dma_zalloc_coherent(xhci_to_hcd(xhci)->self.sysdev,
> + size, &erst->erst_dma_addr, flags);
> if (!erst->entries)
> return -ENOMEM;
>
> - memset(erst->entries, 0, size);
> erst->num_entries = evt_ring->num_segs;
>
> seg = evt_ring->first_seg;
>

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