On Tue, Sep 24, 2019 at 10:47:28AM -0700, Nick Desaulniers wrote: > Fixes the following 2 issues in the driver: > 1. Left shifting a signed integer is undefined behavior. Unsigned > integral types should be used for bitwise operations. > 2. The delay scales from 0x0010 to 0x20000 by powers of 2, but udelay > will result in a linkage failure when given a constant that's greater > than 20000 (0x4E20). Agressive loop unrolling can fully unroll the > loop, resulting in later iterations overflowing the call to udelay. > > 2 is fixed via splitting the loop in two, iterating the first up to the > point where udelay would overflow, then switching to mdelay, as > suggested in Documentation/timers/timers-howto.rst. > > Reported-by: Tomasz Paweł Gajc <tpgxyz@xxxxxxxxx> > Link: https://github.com/ClangBuiltLinux/linux/issues/678 > Debugged-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > Changes V1 -> V2: > * The first loop in send_byte() needs to break out on the same condition > now. Technically, the loop condition could even be removed. The diff > looks funny because of the duplicated logic between existing and newly > added for loops. > > drivers/hwmon/applesmc.c | 35 +++++++++++++++++++++++++++++++---- > 1 file changed, 31 insertions(+), 4 deletions(-) > > diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c > index 183ff3d25129..c76adb504dff 100644 > --- a/drivers/hwmon/applesmc.c > +++ b/drivers/hwmon/applesmc.c > @@ -46,6 +46,7 @@ > #define APPLESMC_MIN_WAIT 0x0010 > #define APPLESMC_RETRY_WAIT 0x0100 > #define APPLESMC_MAX_WAIT 0x20000 > +#define APPLESMC_UDELAY_MAX 20000 > > #define APPLESMC_READ_CMD 0x10 > #define APPLESMC_WRITE_CMD 0x11 > @@ -157,14 +158,23 @@ static struct workqueue_struct *applesmc_led_wq; > static int wait_read(void) > { > u8 status; > - int us; > - for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) { > + unsigned int us; > + > + for (us = APPLESMC_MIN_WAIT; us < APPLESMC_UDELAY_MAX; us <<= 1) { > udelay(us); > status = inb(APPLESMC_CMD_PORT); > /* read: wait for smc to settle */ > if (status & 0x01) > return 0; > } > + /* switch to mdelay for longer sleeps */ > + for (; us < APPLESMC_MAX_WAIT; us <<= 1) { > + mdelay(us); > + status = inb(APPLESMC_CMD_PORT); > + /* read: wait for smc to settle */ > + if (status & 0x01) > + return 0; > + } > > pr_warn("wait_read() fail: 0x%02x\n", status); > return -EIO; > @@ -177,10 +187,10 @@ static int wait_read(void) > static int send_byte(u8 cmd, u16 port) > { > u8 status; > - int us; > + unsigned int us; > > outb(cmd, port); > - for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) { > + for (us = APPLESMC_MIN_WAIT; us < APPLESMC_UDELAY_MAX; us <<= 1) { > udelay(us); > status = inb(APPLESMC_CMD_PORT); > /* write: wait for smc to settle */ > @@ -190,6 +200,23 @@ static int send_byte(u8 cmd, u16 port) > if (status & 0x04) > return 0; > /* timeout: give up */ > + if (us << 1 == APPLESMC_UDELAY_MAX) > + break; > + /* busy: long wait and resend */ > + udelay(APPLESMC_RETRY_WAIT); > + outb(cmd, port); > + } > + /* switch to mdelay for longer sleeps */ > + for (; us < APPLESMC_MAX_WAIT; us <<= 1) { > + mdelay(us); > + status = inb(APPLESMC_CMD_PORT); > + /* write: wait for smc to settle */ > + if (status & 0x02) > + continue; > + /* ready: cmd accepted, return */ > + if (status & 0x04) > + return 0; > + /* timeout: give up */ > if (us << 1 == APPLESMC_MAX_WAIT) > break; > /* busy: long wait and resend */ > -- > 2.23.0.351.gc4317032e6-goog > This resolves the __bad_udelay appearance at -O3 for me. I am not familiar enough with this code to give a reviewed by though! Also, for some odd reason, I couldn't apply your patch with 'git apply': % curl -LSs https://lore.kernel.org/lkml/20190924174728.201464-1-ndesaulniers@xxxxxxxxxx/raw | git apply error: corrupt patch at line 117 It looks like some of the '=' got changed into =3D and some spaces got changed into =20. Weird encoding glitch? Cheers, Nathan
