Messages in this thread | | | Date | Mon, 04 Nov 2013 11:02:22 -0800 | From | David Cohen <> | Subject | Re: [PATCH v3 2/3] usb: ffs: check quirk to pad epout buf size when not aligned to maxpacketsize |
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Hi Alan,
Appreciate your comments. Please, see my reply.
On 10/30/2013 10:35 AM, Alan Stern wrote: > On Wed, 30 Oct 2013, David Cohen wrote: > >> Check gadget.quirk_ep_out_aligned_size to decide if buffer size requires >> to be aligned to maxpacketsize of an out endpoint. ffs_epfile_io() needs >> to pad epout buffer to match above condition if quirk is found. >> >> Signed-off-by: David Cohen <david.a.cohen@linux.intel.com> >> --- >> drivers/usb/gadget/f_fs.c | 17 +++++++++++++++++ >> 1 file changed, 17 insertions(+) >> >> diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c >> index 75e4b78..b49dd55 100644 >> --- a/drivers/usb/gadget/f_fs.c >> +++ b/drivers/usb/gadget/f_fs.c >> @@ -755,10 +755,12 @@ static ssize_t ffs_epfile_io(struct file *file, >> char __user *buf, size_t len, int read) >> { >> struct ffs_epfile *epfile = file->private_data; >> + struct usb_gadget *gadget = epfile->ffs->gadget; >> struct ffs_ep *ep; >> char *data = NULL; >> ssize_t ret; >> int halt; >> + size_t orig_len = len; >> >> goto first_try; >> do { >> @@ -794,6 +796,21 @@ first_try: >> goto error; >> } >> >> + /* >> + * Controller requires buffer size to be aligned to >> + * maxpacketsize of an out endpoint. >> + */ >> + if (gadget->quirk_ep_out_aligned_size && read && >> + !IS_ALIGNED(len, ep->ep->desc->wMaxPacketSize)) { > > IS_ALIGNED works only when the second argument is a power of 2. > > Interrupt endpoints are not required to have maxpacket sizes that are > powers of 2. Does this code ever get used for an interrupt endpoint?
That's a good point. It won't use interrupt ep on the case I am working on, but f_fs allows it. I'll cover both cases in next patchset.
> >> + size_t old_len = len; > > Why add old_len here when you added orig_len above?
See below.
> >> + len = roundup(orig_len, >> + (size_t)ep->ep->desc->wMaxPacketSize); >> + if (unlikely(data) && len > old_len) { > > If the original value wasn't aligned, how can len fail to be > old_len?
This code is inside a loop. There is an unlikely case explained in the end to loop again if ep got disabled or changed while acquiring mutex. If that happens, I want to avoid to re-allocate buffer if previous size was already enough. Since 'len' gets updated when aligning buf size, we need to keep track of 'orig_len' to do only minimum necessary pad on new alignment. 'old_len' is used to save previous value to decide for new allocation or not. But maybe I should change it to something more accurate like 'buf_size' or 'alloc_size'.
Br, David Cohen
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