Hello, I just realized that our current strategy for MBIM backwards compatibility results in bad user experience by *forcing* the user to cdc_mbim if it is enabled at build time. There are legitimate reasons for a user to select cdc_ncm instead of cdc_mbim at runtime, and at the moment we prevent that. The most obvious and important reason is that the required MBIM userspace applications are not ready yet. But even in a future where these are available, I believe we should leave the choice up to the user. So our current build time based decision will not do. But what will? Is a cdc_ncm module param setting MBIM vs NCM priority OK? We could still make the default depend on whether cdc_mbim is built. I don't think there are any reasons to complicate this with a per-device selection. It is really a system wide setting depending on whether MBIM is supported by the system. What do you think? This problem just came up as a result of a user failing to make Linux v3.8 work on a Lenovo Thinkpad X230 with an Ericsson H5321gw Mobile Broadband Device, while v3.7 appeared to work fine. The H5321gw firmware support NCM backwards compatibility, making it work fine with cdc_ncm in v3.7. But in v3.8 we select the cdc_mbim alternate setting instead, and ModemManager does not yet know how to handle that, making it fail. The user noticed the new cdc_mbim module and tried blacklisting it, as one would find natural. But to no effect, as the problem is in the MBIM compatibility check in cdc_ncm. There appears to be no way to force the cdc_ncm driver in v3.8 to be used for this device if cdc_mbim is selected at build time. Which of course is a distro choice and not something most users will touch. I believe we need to resolve this quickly, and I'll probably just cook up a proposed module param patch unless someone comes up with something better. BTW, I am starting to hate the NCM backward compatibility. There were so many other ways this could have been solved. Changing class depending on the selected interface altsetting is ugly, IMHO. Bjørn -- 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
