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SubjectRe: [PATCH v3 2/3] usb: ffs: check quirk to pad epout buf size when not aligned to maxpacketsize
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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