On Tuesday 16 September 2008, Dmitry Torokhov wrote:
> 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...
Looks OK to me ... sorry for the delayed response.
Nicolas: this may be useful on the at91sam926[03] EK boards.
>
> --
> 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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