On Tue, Mar 09, 2010 at 05:39:28PM +0200, Roger Quadros wrote: > ext Greg KH wrote: > >On Tue, Mar 09, 2010 at 05:16:40PM +0200, Felipe Balbi wrote: > >>On Tue, Mar 09, 2010 at 06:54:30AM -0800, Greg KH wrote: > >>>Why is this needed? Why not just use the serial driver instead? That > >>>should provide you with exactly the same end result, right? > >>we experienced several problems with tty layer. The biggest of them is > >>a race between flush_to_ldisc() and ->receiv_buf() which makes the line > >>discipline (I guess only n_tty) loose bytes in some circumstances. > > > >That sounds like a bug we need to fix then, right? > > > >>On top of that there's also the performance issues with tty. the > >>u_serial.c forces us to push each bMaxPacketSize packet to the > >>controller driver which prevents us from actually getting some good deal > >>out of the DMA engine. With u_char.c we are unloading based on what's in > >>the kfifo right now (maybe we should use PAGE_SIZE transfers since our > >>kfifo is allocated using vmalloc()), and we can easily optimize that on > >>a per-product basis. > > > >Then why not just fix u_serial.c to push the same ammount of data? > > > >>Performance is a key concept here; specially when we need to flash > >>hundreds of thousands of devices in a production line. Every milisecond > >>counts. > > > >Sure, I understand, but it seems like it is easier to fix the existing > >code for these minor things, than to write a whole new driver, right? > > > >If you do that, then the existing users will also benifit from those > >changes. > > hi Greg, > > We also needed the following from MTP point of view > 1) ability to handle ioctls in gadget driver > 2) capability to send ZLP/SLP (zero/short length packets) at > precisely the correct point in the data stream. > 3) capability to send events received on EP0 to user space. > > Is it good/possible to have these done in existing TTY framework? No. What's wrong with the gadgetfs interface for custom things such as this? You shouldn't need a special kernel driver for it, right? thanks, greg k-h -- 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
