On Fri, Oct 16, 2015 at 8:27 AM, Johan Hovold <johan@xxxxxxxxxx> wrote: > On Thu, Oct 15, 2015 at 06:23:31PM -0500, Konstantin Shkolnyy wrote: >> cp2108 GET_LINE_CTL returns the 16-bit value with the 2 bytes swapped. >> However, SET_LINE_CTL functions properly. When the driver tries to modify >> the register, it reads it, modifies some bits and writes back. Because the >> read bytes were swapped, this often results in an invalid value to be written. >> In turn, this causes cp2108 respond with a stall. The stall sometimes doesn't >> clear properly and cp2108 starts responding to following valid commands also >> with stalls, effectively failing. > > That sounds weird. Are you saying that all or only some cp2108 devices > would be affected by this? And only for the line-control register? The bug exists in all current cp2108 devices and affects only GET_LINE_CTL. But it may be fixed in a future revision. > What is the endianess of your host by the way? I'm using an Intel-based Dell desktop, so its LE. [...] >> @@ -343,6 +344,10 @@ static int cp210x_get_config(struct usb_serial_port *port, u8 request, >> return result; >> } >> >> + /* Workaround for swapped bytes in 16-bit value from CP210X_GET_LINE_CTL */ >> + if (spriv->swap_get_line_ctl && request == CP210X_GET_LINE_CTL && size == 2) >> + swab16s((u16 *)data); >> + > > If we determine we need this, then it should probably be isolated to a > dedicated line-control helper function. I feel that you want to kill cp210x_get_config. I can easily see why you don't like it :-) I'll gladly replace all "cp210x_get_config(GET_LINE_CTL)" calls with a new "cp210x_get_line_ctl" helper if you don';t mind. [...] >> + port = serial->port[0]; >> >> spriv = kzalloc(sizeof(*spriv), GFP_KERNEL); >> if (!spriv) >> return -ENOMEM; >> >> + /* get_config and set_config rely on this spriv field */ >> cur_altsetting = serial->interface->cur_altsetting; >> spriv->bInterfaceNumber = cur_altsetting->desc.bInterfaceNumber; >> >> + /* Detect CP2108 bug and activate workaround. >> + * Write a known good value 0x800, read it back. >> + * If it comes back swapped the bug is detected. >> + */ >> + >> + /* The following get_config won't swap the bytes */ >> + spriv->swap_get_line_ctl = false; >> + >> + /* must be set before calling get_config and set_config */ >> usb_set_serial_data(serial, spriv); >> >> + line_ctl = 0x800; >> + >> + err = cp210x_set_config(port, CP210X_SET_LINE_CTL, &line_ctl, 2); > > Calling port functions before the ports have been fully initialised > isn't very nice, even if it works for this driver. This should probably > be done in a helper function that accesses this register directly (and So usb_control_msg should be fine to call here, right? > perhaps also avoids overwriting the default setting). You mean save and restore the register setting around this bug detection? [...] Thanks, Konstantin -- 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
