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>

1 files changed, 51 insertions, 36 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 6020a7dcce33..b9b7fc6ff1eb 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");