Input: alps - fix compatibility with -funsigned-char

The AlpsPS/2 code previously relied on the assumption that `char` is a
signed type, which was true on x86 platforms (the only place where this
driver is used) before kernel 6.2. However, on 6.2 and later, this
assumption is broken due to the introduction of -funsigned-char as a new
global compiler flag.

Fix this by explicitly specifying the signedness of `char` when sign
extending the values received from the device.

Fixes: f3f33c677699 ("Input: alps - Rushmore and v7 resolution support")
Signed-off-by: msizanoen <msizanoen@qtmlabs.xyz>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230320045228.182259-1-msizanoen@qtmlabs.xyz
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index 989228b5a0a44d050fa83f291d7c2bd32b576a1e..e2c11d9f3868f3ea2ec05a4230472070e32d20a4 100644 (file)
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -852,8 +852,8 @@ static void alps_process_packet_v6(struct psmouse *psmouse)
                        x = y = z = 0;
 
                /* Divide 4 since trackpoint's speed is too fast */
-               input_report_rel(dev2, REL_X, (char)x / 4);
-               input_report_rel(dev2, REL_Y, -((char)y / 4));
+               input_report_rel(dev2, REL_X, (s8)x / 4);
+               input_report_rel(dev2, REL_Y, -((s8)y / 4));
 
                psmouse_report_standard_buttons(dev2, packet[3]);
 
@@ -1104,8 +1104,8 @@ static void alps_process_trackstick_packet_v7(struct psmouse *psmouse)
            ((packet[3] & 0x20) << 1);
        z = (packet[5] & 0x3f) | ((packet[3] & 0x80) >> 1);
 
-       input_report_rel(dev2, REL_X, (char)x);
-       input_report_rel(dev2, REL_Y, -((char)y));
+       input_report_rel(dev2, REL_X, (s8)x);
+       input_report_rel(dev2, REL_Y, -((s8)y));
        input_report_abs(dev2, ABS_PRESSURE, z);
 
        psmouse_report_standard_buttons(dev2, packet[1]);
@@ -2294,20 +2294,20 @@ static int alps_get_v3_v7_resolution(struct psmouse *psmouse, int reg_pitch)
        if (reg < 0)
                return reg;
 
-       x_pitch = (char)(reg << 4) >> 4; /* sign extend lower 4 bits */
+       x_pitch = (s8)(reg << 4) >> 4; /* sign extend lower 4 bits */
        x_pitch = 50 + 2 * x_pitch; /* In 0.1 mm units */
 
-       y_pitch = (char)reg >> 4; /* sign extend upper 4 bits */
+       y_pitch = (s8)reg >> 4; /* sign extend upper 4 bits */
        y_pitch = 36 + 2 * y_pitch; /* In 0.1 mm units */
 
        reg = alps_command_mode_read_reg(psmouse, reg_pitch + 1);
        if (reg < 0)
                return reg;
 
-       x_electrode = (char)(reg << 4) >> 4; /* sign extend lower 4 bits */
+       x_electrode = (s8)(reg << 4) >> 4; /* sign extend lower 4 bits */
        x_electrode = 17 + x_electrode;
 
-       y_electrode = (char)reg >> 4; /* sign extend upper 4 bits */
+       y_electrode = (s8)reg >> 4; /* sign extend upper 4 bits */
        y_electrode = 13 + y_electrode;
 
        x_phys = x_pitch * (x_electrode - 1); /* In 0.1 mm units */