| Message ID | 20200507102521.17602-1-baijiaju1990@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | media: usb: ttusb-dec: reduce the number of memory reads in ttusb_dec_handle_irq() | expand |
On Thu, May 07, 2020 at 06:25:21PM +0800, Jia-Ju Bai wrote: > In ttusb_dec_handle_irq(), buffer[4] is continuously read from memory > three times, without being modified. > To reduce the number of memory reads, buffer[4] is first assigned to a > local variable index, and then index is used to replace buffer[4]. > > Signed-off-by: Jia-Ju Bai <baijiaju1990@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; > + int 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)) { > - 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); > input_sync(dec->rc_input_dev); > } > } > -- > 2.17.1 > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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; + int 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)) { - 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); input_sync(dec->rc_input_dev); } }
In ttusb_dec_handle_irq(), buffer[4] is continuously read from memory three times, without being modified. To reduce the number of memory reads, buffer[4] is first assigned to a local variable index, and then index is used to replace buffer[4]. Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> --- drivers/media/usb/ttusb-dec/ttusb_dec.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)