linux-kernel - re: usb: gadget: Add support for USB MIDI 2.0 function driver

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Message-ID: <5f54ffd0-b5fe-4203-a626-c166becad362@gmail.com>
Date: Thu, 7 Nov 2024 12:30:12 +0000
From: "Colin King (gmail)" <colin.i.king@...il.com>
To: Takashi Iwai <tiwai@...e.de>
Cc: Paul Cercueil <paul@...pouillou.net>,
 Simona Vetter <simona.vetter@...ll.ch>,
 Christian König <christian.koenig@....com>,
 Michael Grzeschik <m.grzeschik@...gutronix.de>, linux-usb@...r.kernel.org,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: usb: gadget: Add support for USB MIDI 2.0 function driver

Hi,

Static analysis has found a minor issue in the following commit:

commit 8b645922b22303cec4628dbbbf6c8553d1cdec87
Author: Takashi Iwai <tiwai@...e.de>
Date:   Tue Jul 25 08:22:00 2023 +0200

     usb: gadget: Add support for USB MIDI 2.0 function driver

The issue is in function f_midi2_set_alt in 
drivers/usb/gadget/function/f_midi2.c as follows:

         if (intf != midi2->midi_if || alt > 1)
                 return 0;

         if (alt == 0)
                 op_mode = MIDI_OP_MODE_MIDI1;
         else if (alt == 1)
                 op_mode = MIDI_OP_MODE_MIDI2;
         else
                 op_mode = MIDI_OP_MODE_UNSET;

the first if statement will return if alt is 2 or more, so at the 
following cascaded if/else if/else statement alt is either 0 or 1, hence 
the final else that sets op_mode = MIDI_OP_MODE_UNSET can never be 
reached.

Either the last else statement is redundant and can be removed, or the 
first if statement needs to check for alt > 2 rather than > 1. I'm not 
sure which one is the valid fix to make. Any ideas?

Colin