On Fri, 2014-04-11 at 06:51 +0800, Xiao Jin wrote: > Hi, Oliver, > > On 04/10/2014 04:02 PM, Oliver Neukum wrote: > > On Wed, 2014-04-09 at 22:57 +0800, Xiao Jin wrote: > >> Thanks all for the review. We meet with the problems when developing > >> product. I would like to explain my understanding. > >> > >> On 04/08/2014 11:05 AM, Xiao Jin wrote: > >>> > >>> We find two problems on acm tty write delayed mechanism. > >>> (1) When acm resume, the delayed wb will be started. But now > >>> only one write can be saved during acm suspend. More acm write > >>> may be abandoned. > >> > >> The scenario usually happened when user space write series AT after acm > >> suspend. If acm accept the first AT, what's the reason for acm to refuse > >> the second AT? If write return 0, user space will try repeatedly until > >> resume. It looks simpler that acm accept all the data and sent out urb > >> when resume. > > > > No. We cannot accept an arbitrary amount of data. It would let any > > user OOM the system. There will have to be an arbitrary limit. > > The simplest limit is 1 urb. And that is because we said that we > > are ready to accept data. > > > > We apply cdc-acm for modem AT data. I can find other usb modem driver > usb_wwan_write use list to accept more data when suspend, maybe usbnet > is the same. Do you have any more reason for me to understand why > cdc-acm accept only one? User space must be ready to deal with a device that cannot accept any more data. There is simply no additional benefit in more caching. > We see tty write and close concurrently, we have debug log to show that > acm_tty_write and acm_resume is called after acm_port_shutdown, I don't > understand "resuming the device in shutdown() should do the job". There we have a problem. In fact it looks like a bug in the tty layer. Could you post the logs? Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
