5.4-stable review patch. If anyone has any objections, please let me know.
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From: Zicheng Qu quzicheng@huawei.com
commit c0599762f0c7e260b99c6b7bceb8eae69b804c94 upstream.
User Perspective: When a user sets the phase value, the ad9834_write_phase() is called. The phase register has a 12-bit resolution, so the valid range is 0 to 4095. If the phase offset value of 4096 is input, it effectively exactly equals 0 in the lower 12 bits, meaning no offset.
Reasons for the Change: 1) Original Condition (phase > BIT(AD9834_PHASE_BITS)): This condition allows a phase value equal to 2^12, which is 4096. However, this value exceeds the valid 12-bit range, as the maximum valid phase value should be 4095. 2) Modified Condition (phase >= BIT(AD9834_PHASE_BITS)): Ensures that the phase value is within the valid range, preventing invalid datafrom being written.
Impact on Subsequent Logic: st->data = cpu_to_be16(addr | phase): If the phase value is 2^12, i.e., 4096 (0001 0000 0000 0000), and addr is AD9834_REG_PHASE0 (1100 0000 0000 0000), then addr | phase results in 1101 0000 0000 0000, occupying DB12. According to the section of WRITING TO A PHASE REGISTER in the datasheet, the MSB 12 PHASE0 bits should be DB11. The original condition leads to incorrect DB12 usage, which contradicts the datasheet and could pose potential issues for future updates if DB12 is used in such related cases.
Fixes: 12b9d5bf76bf ("Staging: IIO: DDS: AD9833 / AD9834 driver") Cc: stable@vger.kernel.org Signed-off-by: Zicheng Qu quzicheng@huawei.com Reviewed-by: Dan Carpenter dan.carpenter@linaro.org Link: https://patch.msgid.link/20241107011015.2472600-2-quzicheng@huawei.com Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/staging/iio/frequency/ad9834.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/staging/iio/frequency/ad9834.c +++ b/drivers/staging/iio/frequency/ad9834.c @@ -132,7 +132,7 @@ static int ad9834_write_frequency(struct static int ad9834_write_phase(struct ad9834_state *st, unsigned long addr, unsigned long phase) { - if (phase > BIT(AD9834_PHASE_BITS)) + if (phase >= BIT(AD9834_PHASE_BITS)) return -EINVAL; st->data = cpu_to_be16(addr | phase);