2009/3/13 Eric Miao <ymiao3@xxxxxxxxxxx>: > > >> -----Original Message----- >> From: Dmitry Torokhov [mailto:dmitry.torokhov@xxxxxxxxx] >> Sent: 2009年3月13日 10:34 >> To: akpm@xxxxxxxxxxxxxxxxxxxx >> Cc: linux-input@xxxxxxxxxxxxxxx; Eric Miao; david-b@xxxxxxxxxxx >> Subject: Re: [patch 22/22] input: ads7846: introduce platform specific way >> to synchronize sampling >> >> Hi, >> >> On Wed, Mar 04, 2009 at 11:59:13AM -0800, akpm@xxxxxxxxxxxxxxxxxxxx wrote: >> > From: Eric Miao <eric.miao@xxxxxxxxxxx> >> > >> > Noises can be introduced when LCD signals are being driven, some platforms >> > provide a signal to assist the synchronization of this sampling procedure. >> > >> > Signed-off-by: Eric Miao <eric.miao@xxxxxxxxxxx> >> > Cc: David Brownell <david-b@xxxxxxxxxxx> >> > Cc: Dmitry Torokhov <dtor@xxxxxxx> >> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> > --- >> > >> > drivers/input/touchscreen/ads7846.c | 10 ++++++++++ >> > include/linux/spi/ads7846.h | 2 ++ >> > 2 files changed, 12 insertions(+) >> > >> > diff -puN drivers/input/touchscreen/ads7846.c~input-ads7846-introduce- >> platform-specific-way-to-synchronize-sampling >> drivers/input/touchscreen/ads7846.c >> > --- a/drivers/input/touchscreen/ads7846.c~input-ads7846-introduce- >> platform-specific-way-to-synchronize-sampling >> > +++ a/drivers/input/touchscreen/ads7846.c >> > @@ -127,6 +127,8 @@ struct ads7846 { >> > void (*filter_cleanup)(void *data); >> > int (*get_pendown_state)(void); >> > int gpio_pendown; >> > + >> > + void (*wait_for_sync)(void); >> > }; >> > >> > /* leave chip selected when we're done, for quicker re-select? */ >> > @@ -511,6 +513,10 @@ static int get_pendown_state(struct ads7 >> > return !gpio_get_value(ts->gpio_pendown); >> > } >> > >> > +static void null_wait_for_sync(void) >> > +{ >> > +} >> > + >> > /* >> > * PENIRQ only kicks the timer. The timer only reissues the SPI transfer, >> > * to retrieve touchscreen status. >> > @@ -686,6 +692,7 @@ static void ads7846_rx_val(void *ads) >> > default: >> > BUG(); >> > } >> > + ts->wait_for_sync(); >> > status = spi_async(ts->spi, m); >> > if (status) >> > dev_err(&ts->spi->dev, "spi_async --> %d\n", >> > @@ -723,6 +730,7 @@ static enum hrtimer_restart ads7846_time >> > } else { >> > /* pen is still down, continue with the measurement */ >> > ts->msg_idx = 0; >> > + ts->wait_for_sync(); >> >> We are in hard IRQ context here. What is the expectation of >> wait_for_sync()? How long are we waiting here? >> > > This should be a workaround for broken hardware and I don't expect > this sync time on every boards. > The sync time depends on the moment of this sync between two HSYNC, I don't expect that to be very long, yet the hardware is broken enough to endure this latency. -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
