On Mon, 24 Apr 2006 11:55:51 -0400 (EDT), Alan Stern <[EMAIL PROTECTED]> wrote:
> Before submitting the patch, it seemed like a good idea to check with you > and make sure it doesn't cause any problems. I'd appreciate it if you > could try it out and let me know what happens. The patch is based on > 2.6.17-rc2. Everything works fine here. I verified briefly that USBR do not get stuck and that performace is adquate. The code looks fine though this concerns me a little: > + __le32 old_status, new_status, hw_status; > + > + /* Do this carefully because the hardware might > + * be updating td->status right now. There's still > + * a race because the controller might already have > + * fetched the old value and be almost ready to > + * overwrite the IOC with a new value. Nothing > + * much we can do if that happens. */ > + old_status = cpu_to_le32(status); > + new_status = cpu_to_le32(status | TD_CTRL_IOC); > + hw_status = cmpxchg(&qh->next_td->status, > + old_status, new_status); > + if (hw_status != old_status) > + goto restart; > + } The cmpxchg() is a second class citizen in platform API, so it may not be implemented, or is implemented without any atomicity guarantees. I'm pretty sure some CPUs cannot make these guarantees when they contend with device DMA rather than other CPUs. I don't know what to do about this. It's tempting to ignore the issue and say that owners of obscure platforms deserve what they get... -- Pete ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
