From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?q?Bj=C3=B8rn=20Mork?= Subject: [PATCH net] net: cdc_mbim: send ZLP only for the specific buggy device Date: Wed, 23 Jan 2013 11:57:02 +0100 Message-ID: <1358938622-18344-1-git-send-email-bjorn@mork.no> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Oliver Neukum , Greg Suarez , =?UTF-8?q?Bj=C3=B8rn=20Mork?= , Alexey ORISHKO , Yauheni Kaliuta To: netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Return-path: Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org Reverting 328d7b8 and instead adding an exception for the Sierra Wireless MC7710. commit 328d7b8 (net: cdc_mbim: send ZLP after max sized NTBs) added a workaround for an issue observed on one specific device. Concerns were raised that this workaround adds a performance penalty to all devices based on questionable, if not buggy, behaviour of a single device: "If you add ZLP for NTBs of dwNtbOutMaxSize, you are heavily affecting= CPU load, increasing interrupt load by factor of 2 in high load traffic scenario and possibly decreasing throughput for all other devices which behaves correctly." "The idea of NCM was to avoid extra ZLPs. If your transfer is exactly dwNtbOutMaxSize, it's known, you can submit such request on the recei= ver side and you do not need any EOT indicatation, so the frametime can b= e used for useful data." Adding a device specific exception to prevent the workaround from affecting well behaved devices. The assumption here is that needing a ZLP is truly an *exception*. We do not yet have enough data to verify this. The generic workaround in commit 328d7b8 should be considered acceptable despite the performance penalty if the exception list becomes a maintainance hassle. Cc: Alexey ORISHKO Cc: Yauheni Kaliuta Signed-off-by: Bj=C3=B8rn Mork --- Sorry about all the back and forth here. And as indicated in the commi= t message, I am not guaranteeing this is the last round either... I am not going to maintain an ever-growing exception list. My personal accptance limit for such lists in a class driver is extremely low. I a= m going to reconsider the original patch the next time a device wants thi= s specific workaround. And I fear that will happen really soon, based on the facts that the device the issue in question=20 - is based on Qualcomm firmware, - is commercially available now, - is just one of a gazillion expected Qualcomm hardware/firmware based MBIM devices on their way to a Linux computer near you... Yes the firmware is of course buggy as hell. We don't expect anything else. But it doesn't matter. If a significant number of MBIM devices from a number of different vendors have the same bug, then we will do what's needed to support them. Including accepting smaller performance penalties not noticable to any end user. In fact not even measurable to anyone without device firmware debugging tools. But please let this go into 3.8 for now, and let us all hope I am wrong this time too, as I often am :-) Bj=C3=B8rn drivers/net/usb/cdc_mbim.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c index 3a5673a..248d2dc 100644 --- a/drivers/net/usb/cdc_mbim.c +++ b/drivers/net/usb/cdc_mbim.c @@ -366,6 +366,21 @@ err: =20 static const struct driver_info cdc_mbim_info =3D { .description =3D "CDC MBIM", + .flags =3D FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN, + .bind =3D cdc_mbim_bind, + .unbind =3D cdc_mbim_unbind, + .manage_power =3D cdc_mbim_manage_power, + .rx_fixup =3D cdc_mbim_rx_fixup, + .tx_fixup =3D cdc_mbim_tx_fixup, +}; + +/* MBIM and NCM devices should not need a ZLP after NTBs with + * dwNtbOutMaxSize length. This driver_info is for the exceptional + * devices requiring it anyway, allowing them to be supported without + * forcing the performance penalty on all the sane devices. + */ +static const struct driver_info cdc_mbim_info_zlp =3D { + .description =3D "CDC MBIM", .flags =3D FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN | FLAG_SEND= _ZLP, .bind =3D cdc_mbim_bind, .unbind =3D cdc_mbim_unbind, @@ -385,6 +400,10 @@ static const struct usb_device_id mbim_devs[] =3D = { { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_NCM, USB_CDC_PR= OTO_NONE), .driver_info =3D (unsigned long)&cdc_mbim_info, }, + /* Sierra Wireless MC7710 need ZLPs */ + { USB_DEVICE_AND_INTERFACE_INFO(0x1199, 0x68a2, USB_CLASS_COMM, USB_C= DC_SUBCLASS_MBIM, USB_CDC_PROTO_NONE), + .driver_info =3D (unsigned long)&cdc_mbim_info_zlp, + }, { USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_MBIM, USB_CDC_P= ROTO_NONE), .driver_info =3D (unsigned long)&cdc_mbim_info, }, --=20 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html