Re: [PATCH 1/2] usb: gadget: f_ncm: do not notify from ncm_set_alt()

[sashiko-bot@kernel.org]

> From: Massimo Toscanelli <massimo.toscanelli@leica-geosystems.com>
> 
> ncm_set_alt() calls ncm_notify() for both altsettings of the data
> interface. So a notification is already queued at SET_CONFIGURATION,
> when altsetting 0 is selected, and it waits until the host reads the
> interrupt endpoint.
> 
> The USB 2.0 LPM ECN (section 2.2.2) lets a device answer NYET to an LPM
> request when it has data pending for the host, and DWC3 does so. So
> when the host loads no class driver, like the USB-IF test tool, the
> device never enters L1 and the LPM L1 test fails.
> 
> The CDC NCM spec (version 1.1, section 9.2) [1] asks for the
> notifications only when the host selects altsetting 1. There the call
> is not needed: gether_connect() already calls ncm_open() or
> ncm_close(), and both notify. The extra call only restarts the
> sequence while the first notification is in flight, so the host gets
> two connection notifications before the speed one.
> 
> The old ether.c also notified only for altsetting 1, until commit
> da741b8c56d6 ("usb ethernet gadget: split CDC Ethernet function")
> moved the call out of that branch in f_ecm. f_ncm copied that
> pattern.
> 
> Remove the call.
> 
> Fixes: 9f6ce4240a2b ("usb: gadget: f_ncm.c added")
> Link: https://www.usb.org/sites/default/files/NCM11.pdf # [1]
> Signed-off-by: Massimo Toscanelli <massimo.toscanelli@leica-geosystems.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261023-ncm-ecm-lpm-v1-0-d01e81fbf460@leica-geosystems.com?part=1