On Mon, Sep 15, 2008 at 04:32:17PM -0700, David Brownell wrote:
> From: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
>
> We had a report a while back that the ads7846 driver had some issues
> when used with DMA-based SPI controllers (like atmel_spi) on systems
> where main memory is not DMA-coherent (most non-x86 boards) ... but no
> mergeable patch addressed it. Pending any more comprehensive fix,
> just push the relevant data into cache lines that won't be shared,
> preventing those issues (but not in a very pretty way).
>
How about this one? Because the change is purely mechanical I feel
pretty safe about it...
--
Dmitry
Input: ads7846 - fix cache line sharing issue
We had a report a while back that the ads7846 driver had some issues
when used with DMA-based SPI controllers (like atmel_spi) on systems
where main memory is not DMA-coherent (most non-x86 boards). Allocate
memory potentially used for DMA separately to avoid cache line issues.
Reported-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dmitry Torokhov <dtor@xxxxxxx>
---
drivers/input/touchscreen/ads7846.c | 87 +++++++++++++++++++++--------------
1 files changed, 51 insertions(+), 36 deletions(-)
diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 6020a7d..b9b7fc6 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -69,6 +69,17 @@ struct ts_event {
int ignore;
};
+/*
+ * We allocate this separately to avoid cache line sharing issues when
+ * driver is used with DMA-based SPI controllers (like atmel_spi) on
+ * systems where main memory is not DMA-coherent (most non-x86 boards).
+ */
+struct ads7846_packet {
+ u8 read_x, read_y, read_z1, read_z2, pwrdown;
+ u16 dummy; /* for the pwrdown read */
+ struct ts_event tc;
+};
+
struct ads7846 {
struct input_dev *input;
char phys[32];
@@ -86,9 +97,7 @@ struct ads7846 {
u16 x_plate_ohms;
u16 pressure_max;
- u8 read_x, read_y, read_z1, read_z2, pwrdown;
- u16 dummy; /* for the pwrdown read */
- struct ts_event tc;
+ struct ads7846_packet *packet;
struct spi_transfer xfer[18];
struct spi_message msg[5];
@@ -513,16 +522,17 @@ static int get_pendown_state(struct ads7846 *ts)
static void ads7846_rx(void *ads)
{
struct ads7846 *ts = ads;
+ struct ads7846_packet *packet = ts->packet;
unsigned Rt;
u16 x, y, z1, z2;
/* ads7846_rx_val() did in-place conversion (including byteswap) from
* on-the-wire format as part of debouncing to get stable readings.
*/
- x = ts->tc.x;
- y = ts->tc.y;
- z1 = ts->tc.z1;
- z2 = ts->tc.z2;
+ x = packet->tc.x;
+ y = packet->tc.y;
+ z1 = packet->tc.z1;
+ z2 = packet->tc.z2;
/* range filtering */
if (x == MAX_12BIT)
@@ -546,10 +556,10 @@ static void ads7846_rx(void *ads)
* the maximum. Don't report it to user space, repeat at least
* once more the measurement
*/
- if (ts->tc.ignore || Rt > ts->pressure_max) {
+ if (packet->tc.ignore || Rt > ts->pressure_max) {
#ifdef VERBOSE
pr_debug("%s: ignored %d pressure %d\n",
- ts->spi->dev.bus_id, ts->tc.ignore, Rt);
+ ts->spi->dev.bus_id, packet->tc.ignore, Rt);
#endif
hrtimer_start(&ts->timer, ktime_set(0, TS_POLL_PERIOD),
HRTIMER_MODE_REL);
@@ -642,6 +652,7 @@ static int ads7846_no_filter(void *ads, int data_idx, int *val)
static void ads7846_rx_val(void *ads)
{
struct ads7846 *ts = ads;
+ struct ads7846_packet *packet = ts->packet;
struct spi_message *m;
struct spi_transfer *t;
int val;
@@ -661,7 +672,7 @@ static void ads7846_rx_val(void *ads)
case ADS7846_FILTER_REPEAT:
break;
case ADS7846_FILTER_IGNORE:
- ts->tc.ignore = 1;
+ packet->tc.ignore = 1;
/* Last message will contain ads7846_rx() as the
* completion function.
*/
@@ -669,7 +680,7 @@ static void ads7846_rx_val(void *ads)
break;
case ADS7846_FILTER_OK:
*(u16 *)t->rx_buf = val;
- ts->tc.ignore = 0;
+ packet->tc.ignore = 0;
m = &ts->msg[++ts->msg_idx];
break;
default:
@@ -774,7 +785,6 @@ static void ads7846_disable(struct ads7846 *ts)
/* we know the chip's in lowpower mode since we always
* leave it that way after every request
*/
-
}
/* Must be called with ts->lock held */
@@ -850,6 +860,7 @@ static int __devinit setup_pendown(struct spi_device *spi, struct ads7846 *ts)
static int __devinit ads7846_probe(struct spi_device *spi)
{
struct ads7846 *ts;
+ struct ads7846_packet *packet;
struct input_dev *input_dev;
struct ads7846_platform_data *pdata = spi->dev.platform_data;
struct spi_message *m;
@@ -885,14 +896,16 @@ static int __devinit ads7846_probe(struct spi_device *spi)
return err;
ts = kzalloc(sizeof(struct ads7846), GFP_KERNEL);
+ packet = kzalloc(sizeof(struct ads7846_packet), GFP_KERNEL);
input_dev = input_allocate_device();
- if (!ts || !input_dev) {
+ if (!ts || !packet || !input_dev) {
err = -ENOMEM;
goto err_free_mem;
}
dev_set_drvdata(&spi->dev, ts);
+ ts->packet = packet;
ts->spi = spi;
ts->input = input_dev;
ts->vref_mv = pdata->vref_mv;
@@ -964,13 +977,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
/* y- still on; turn on only y+ (and ADC) */
- ts->read_y = READ_Y(vref);
- x->tx_buf = &ts->read_y;
+ packet->read_y = READ_Y(vref);
+ x->tx_buf = &packet->read_y;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.y;
+ x->rx_buf = &packet->tc.y;
x->len = 2;
spi_message_add_tail(x, m);
@@ -982,12 +995,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
x->delay_usecs = pdata->settle_delay_usecs;
x++;
- x->tx_buf = &ts->read_y;
+ x->tx_buf = &packet->read_y;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.y;
+ x->rx_buf = &packet->tc.y;
x->len = 2;
spi_message_add_tail(x, m);
}
@@ -1000,13 +1013,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
/* turn y- off, x+ on, then leave in lowpower */
x++;
- ts->read_x = READ_X(vref);
- x->tx_buf = &ts->read_x;
+ packet->read_x = READ_X(vref);
+ x->tx_buf = &packet->read_x;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.x;
+ x->rx_buf = &packet->tc.x;
x->len = 2;
spi_message_add_tail(x, m);
@@ -1015,12 +1028,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
x->delay_usecs = pdata->settle_delay_usecs;
x++;
- x->tx_buf = &ts->read_x;
+ x->tx_buf = &packet->read_x;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.x;
+ x->rx_buf = &packet->tc.x;
x->len = 2;
spi_message_add_tail(x, m);
}
@@ -1034,13 +1047,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
x++;
- ts->read_z1 = READ_Z1(vref);
- x->tx_buf = &ts->read_z1;
+ packet->read_z1 = READ_Z1(vref);
+ x->tx_buf = &packet->read_z1;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.z1;
+ x->rx_buf = &packet->tc.z1;
x->len = 2;
spi_message_add_tail(x, m);
@@ -1049,12 +1062,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
x->delay_usecs = pdata->settle_delay_usecs;
x++;
- x->tx_buf = &ts->read_z1;
+ x->tx_buf = &packet->read_z1;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.z1;
+ x->rx_buf = &packet->tc.z1;
x->len = 2;
spi_message_add_tail(x, m);
}
@@ -1066,13 +1079,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
x++;
- ts->read_z2 = READ_Z2(vref);
- x->tx_buf = &ts->read_z2;
+ packet->read_z2 = READ_Z2(vref);
+ x->tx_buf = &packet->read_z2;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.z2;
+ x->rx_buf = &packet->tc.z2;
x->len = 2;
spi_message_add_tail(x, m);
@@ -1081,12 +1094,12 @@ static int __devinit ads7846_probe(struct spi_device *spi)
x->delay_usecs = pdata->settle_delay_usecs;
x++;
- x->tx_buf = &ts->read_z2;
+ x->tx_buf = &packet->read_z2;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->tc.z2;
+ x->rx_buf = &packet->tc.z2;
x->len = 2;
spi_message_add_tail(x, m);
}
@@ -1100,13 +1113,13 @@ static int __devinit ads7846_probe(struct spi_device *spi)
spi_message_init(m);
x++;
- ts->pwrdown = PWRDOWN;
- x->tx_buf = &ts->pwrdown;
+ packet->pwrdown = PWRDOWN;
+ x->tx_buf = &packet->pwrdown;
x->len = 1;
spi_message_add_tail(x, m);
x++;
- x->rx_buf = &ts->dummy;
+ x->rx_buf = &packet->dummy;
x->len = 2;
CS_CHANGE(*x);
spi_message_add_tail(x, m);
@@ -1159,6 +1172,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
ts->filter_cleanup(ts->filter_data);
err_free_mem:
input_free_device(input_dev);
+ kfree(packet);
kfree(ts);
return err;
}
@@ -1184,6 +1198,7 @@ static int __devexit ads7846_remove(struct spi_device *spi)
if (ts->filter_cleanup)
ts->filter_cleanup(ts->filter_data);
+ kfree(ts->packet);
kfree(ts);
dev_dbg(&spi->dev, "unregistered touchscreen\n");
--
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