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@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 6020a7d..b9b7fc6 100644 (file)
--- 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");