Soewono Effendi wrote:
> Hi Johann,
>
> thanks for your reply.
> Surelly I understand what the codes
>
Sorry, I missed the point of the question.
My guess would be that uhci_hub_status_data should return len, perhaps ?
This variable is computed, but not used, apparently. It would make sense
to return the length of the buffer returned.
>>> return !!*buf;
>>
> literally mean.
>
> What I would like to know is, what does it suppose to do in context of USB layer.
> If one follows the USB codes, then one will see that this "uhci_hub_status_data"
> will be called by rh_report_status() in usb/core/hcd.c as shown below:
>
> /* timer callback */
>
> static void rh_report_status (unsigned long ptr)
> {
> ...
>
> if (HCD_IS_RUNNING (hcd->state)) {
> length = hcd->driver->hub_status_data (hcd,
> urb->transfer_buffer);
> spin_unlock_irqrestore (&urb->lock, flags);
> if (length > 0) {
> urb->actual_length = length;
> urb->status = 0;
> urb->complete (urb);
> }
> spin_lock_irqsave (&hcd_data_lock, flags);
> urb->status = -EINPROGRESS;
>
>
> ...
> }
>
>
> As far as I can understand from UHCI Specs, this following line will query the
>enabled/disabled status of UHCI ports:
>
>>> *buf |= ((inw(io_addr + USBPORTSC1 + i * 2) & 0xa) > 0 ? (1 << (i
>+ 1)) : 0);
>>
>
> thus it is not an indication of the real "urb->actual_length".
> Maybe it is supposed to force "urb->complete(urb)" to be called on the ports' status
>changing.
>
> These kind of "not obvious" purposes seem sadly to be common in kernel sources.
> Little notes in code will be really helpful.
>
> Best regards,
> sE
>
> On Wed, 24 Jul 2002 10:47:12 +0200
> "Johann Deneux" <[EMAIL PROTECTED]> wrote:
>
>
>>Soewono Effendi wrote:
>>
>>>Hi all,
>>>
>>>
>>>I'm just curious if there is any particular reason to use the following code
>>>
>>> return !!*buf;
>>>
>>>instead of the simple
>>>
>>> return (int) *buf;
>>>
>>
>>This would be a trick to return 0 or 1.
>>Take for example *buf equal to 3.
>>!*buf -> !3 -> !(true) -> false -> 0
>>!!*buf -> !0 -> 1
>>
>>return !!*buf returns 1, while return (int) *buf returns 3;
>>
>>
>>>in function "uhci_hub_status_data", file: usb/host/uhci-hub.c
>>>
>>>static int uhci_hub_status_data(struct usb_hcd *hcd, char *buf)
>>>{
>>> struct uhci_hcd *uhci = hcd_to_uhci(hcd);
>>> unsigned int io_addr = uhci->io_addr;
>>> int i, len = 1;
>>>
>>> *buf = 0;
>>> for (i = 0; i < uhci->rh_numports; i++) {
>>> *buf |= ((inw(io_addr + USBPORTSC1 + i * 2) & 0xa) > 0 ? (1 << (i
>+ 1)) : 0);
>>> len = (i + 1) / 8 + 1;
>>> }
>>>
>>> return !!*buf;
>>>}
>>>
>>>
>>>Little notes in code will be helpful.
>>>
>>>Best regards,
>>>sE
>>>
>>
>>
>>
>>--
>>Johann Deneux
>
>
>
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--
Johann Deneux
PhD student at Uppsala University, Algorithmic Program Verification
http://www.docs.uu.se/~johannd
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