On Fri, 27 Jan 2023, at 8:29 PM, Richard Kjerstadius wrote: > Prior to this patch, the bitmask ends up being 0x3, as opposed to 0x1 > which likely was the intention. The erroneous bit results in the driver > reporting 2 different button activations in designs with 2 or more > buttons. > > To detect which button has been pressed, cyttsp5_btn_attention() uses a > for loop to iterate through the input buffer, while shifting and > applying a bitmask to determine the state for each button. > Unfortunately, when the bitmask is 0x3 and there are multiple buttons, > this procedure falls apart. > > Consider a design with 3 buttons. Pressing the third button will result > in a call to cyttsp5_btn_attention() with the input buffer containing > 0x4 (binary 0100). In the first iteration of the for loop cur_btn_state > will be: > > (0x4 >> 0 * 1) & 0x3 = 0x4 & 0x3 = 0x0 > > This is correct. However, in the next iteration this happens: > > (0x4 >> 1 * 1) & 0x3 = 0x2 & 0x3 = 0x2 > > Which means that a key event for key 1 is generated, even though it's > not really active. In the third iteration, the loop detects the button > that was actually pressed: > > (0x4 >> 2 * 1) & 0x3 = 0x1 & 0x3 = 0x1 > > This key event is the only one that should have been detected, but it is > accompanied by the preceding key. Ensuring the applied mask is 0x1 > solves this problem. > > Signed-off-by: Richard Kjerstadius <richard.kjerstadius@xxxxxxxxxxxx> Reviewed-by: Alistair Francis <alistair@xxxxxxxxxxxxx> Alistair > --- > drivers/input/touchscreen/cyttsp5.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/input/touchscreen/cyttsp5.c b/drivers/input/touchscreen/cyttsp5.c > index 4a23d6231382..16caffa35dd9 100644 > --- a/drivers/input/touchscreen/cyttsp5.c > +++ b/drivers/input/touchscreen/cyttsp5.c > @@ -29,7 +29,7 @@ > #define CY_MAX_INPUT 512 > #define CYTTSP5_PREALLOCATED_CMD_BUFFER 32 > #define CY_BITS_PER_BTN 1 > -#define CY_NUM_BTN_EVENT_ID GENMASK(CY_BITS_PER_BTN, 0) > +#define CY_NUM_BTN_EVENT_ID GENMASK(CY_BITS_PER_BTN - 1, 0) > > #define MAX_AREA 255 > #define HID_OUTPUT_BL_SOP 0x1 > -- > 2.39.0 > >
