On Wed, Jul 31, 2019 at 12:28:55AM +1000, Michael Ellerman wrote: > Stephen Rothwell <s...@canb.auug.org.au> writes: > > Mark switch cases where we are expecting to fall through. > > > > This patch fixes the following warning (Building: powerpc): > > > > drivers/macintosh/smu.c: In function 'smu_queue_i2c': > > drivers/macintosh/smu.c:854:21: warning: this statement may fall through > > [-Wimplicit-fallthrough=] > > cmd->info.devaddr &= 0xfe; > > ~~~~~~~~~~~~~~~~~~^~~~~~~ > > drivers/macintosh/smu.c:855:2: note: here > > case SMU_I2C_TRANSFER_STDSUB: > > ^~~~ > > > > Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > Cc: Gustavo A. R. Silva <gust...@embeddedor.com> > > Cc: Kees Cook <keesc...@chromium.org> > > Signed-off-by: Stephen Rothwell <s...@canb.auug.org.au> > > --- > > drivers/macintosh/smu.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/drivers/macintosh/smu.c b/drivers/macintosh/smu.c > > index 276065c888bc..23f1f41c8602 100644 > > --- a/drivers/macintosh/smu.c > > +++ b/drivers/macintosh/smu.c > > @@ -852,6 +852,7 @@ int smu_queue_i2c(struct smu_i2c_cmd *cmd) > > break; > > case SMU_I2C_TRANSFER_COMBINED: > > cmd->info.devaddr &= 0xfe; > > + /* fall through */ > > case SMU_I2C_TRANSFER_STDSUB: > > if (cmd->info.sublen > 3) > > return -EINVAL; > > Why do we think it's an expected fall through? I can't really convince > myself from the surrounding code that it's definitely intentional.
Yeah, good question. Just now when I went looking for who used SMU_I2C_TRANSFER_COMBINED, I found the only caller in arch/powerpc/platforms/powermac/low_i2c.c and it is clearly using a fall-through for building the command for "stdsub" and "combined", so I think that's justification enough: switch(bus->mode) { case pmac_i2c_mode_std: if (subsize != 0) return -EINVAL; cmd->info.type = SMU_I2C_TRANSFER_SIMPLE; break; case pmac_i2c_mode_stdsub: case pmac_i2c_mode_combined: if (subsize > 3 || subsize < 1) return -EINVAL; cmd->info.sublen = subsize; /* that's big-endian only but heh ! */ memcpy(&cmd->info.subaddr, ((char *)&subaddr) + (4 - subsize), subsize); if (bus->mode == pmac_i2c_mode_stdsub) cmd->info.type = SMU_I2C_TRANSFER_STDSUB; else cmd->info.type = SMU_I2C_TRANSFER_COMBINED; Reviewed-by: Kees Cook <keesc...@chromium.org> -- Kees Cook