Thanks for the reply, Sean :)

On 2020/5/7 16:43, Sean Young wrote:
On Tue, May 05, 2020 at 10:21:10PM +0800, Jia-Ju Bai wrote:
Signed-off-by: Jia-Ju Bai <baijiaju1...@gmail.com>
---
  drivers/media/usb/ttusb-dec/ttusb_dec.c | 9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/ttusb-dec/ttusb_dec.c 
b/drivers/media/usb/ttusb-dec/ttusb_dec.c
index 3198f9624b7c..8543c552515b 100644
--- a/drivers/media/usb/ttusb-dec/ttusb_dec.c
+++ b/drivers/media/usb/ttusb-dec/ttusb_dec.c
@@ -250,6 +250,7 @@ static void ttusb_dec_handle_irq( struct urb *urb)
        struct ttusb_dec *dec = urb->context;
        char *buffer = dec->irq_buffer;
        int retval;
+       u8 index = buffer[4];
switch(urb->status) {
                case 0: /*success*/
@@ -281,11 +282,11 @@ static void ttusb_dec_handle_irq( struct urb *urb)
                 * this should/could be added later ...
                 * for now lets report each signal as a key down and up
                 */
-               if (buffer[4] - 1 < ARRAY_SIZE(rc_keys)) {
Here buffer[4] is signed char, so if buffer[4] == 0 then (buffer[4] - 1) = -1,
this becomes "if (-1 < ARRAY_SIZE(rc_keys))", which evaluates to false,
due to it becoming an unsigned compare. _I think_.

I think you are right.
Maybe I should use "int index = buffer[4]" here.

-                       dprintk("%s:rc signal:%d\n", __func__, buffer[4]);
-                       input_report_key(dec->rc_input_dev, rc_keys[buffer[4] - 
1], 1);
+               if (index - 1 < ARRAY_SIZE(rc_keys)) {
+                       dprintk("%s:rc signal:%d\n", __func__, index);
+                       input_report_key(dec->rc_input_dev, rc_keys[index - 1], 
1);
                        input_sync(dec->rc_input_dev);
-                       input_report_key(dec->rc_input_dev, rc_keys[buffer[4] - 
1], 0);
+                       input_report_key(dec->rc_input_dev, rc_keys[index - 1], 
0);
Like Greg said, this patch reduces the number of dereferences and makes
the code much cleaner, but the commit message is misleading.

Okay, I will change my log and send a new patch.


Best wishes,
Jia-Ju Bai

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