On Sun, Mar 12, 2023 at 05:23:47PM -0400, William Breathitt Gray wrote:
The Counter (CNTR) register is 24 bits wide, but we can have an effective 25-bit count value by setting bit 24 to the XOR of the Borrow flag and Carry flag. The flags can be read from the FLAG register, but a race condition exists: the Borrow flag and Carry flag are instantaneous and could change by the time the count value is read from the CNTR register.
Since the race condition could result in an incorrect 25-bit count value, remove support for 25-bit count values from this driver; hard-coded maximum count values are replaced by a LS7267_CNTR_MAX define for consistency and clarity.
Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8") Cc: stable@vger.kernel.org Signed-off-by: William Breathitt Gray william.gray@linaro.org @@ -156,19 +155,9 @@ static int quad8_count_read(struct counter_device *counter, { struct quad8 *const priv = counter_priv(counter); struct channel_reg __iomem *const chan = priv->reg->channel + count->id;
- unsigned int flags;
- unsigned int borrow;
- unsigned int carry; unsigned long irqflags; int i;
- flags = ioread8(&chan->control);
- borrow = flags & QUAD8_FLAG_BT;
- carry = !!(flags & QUAD8_FLAG_CT);
- /* Borrow XOR Carry effectively doubles count range */
- *val = (unsigned long)(borrow ^ carry) << 24;
The count value is used later on so it should be initialized here; I'll submit a v3 along with some backports as well for the other stable kernels.
William Breathitt Gray