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Subject[PATCH v9 42/55] Input: atmel_mxt_ts: Limit the max bytes transferred in an i2c transaction
Date
From: Balasubramani Vivekanandan <balasubramani_vivekanandan@mentor.com>

In mxt_process_messages_until_invalid() function, driver tries to read
all possible reportid in a single i2c transaction. Number of bytes read
is limited by the max_reportid parameter.
If the max_reportid is a very large value, then a large chunk of bytes
will be requested from the controller in a single i2c transaction.
This transaction can fail due to timeout. This is visible when the
Atmel controller is connected to the SOC via a i2c mux hardware.

mxt_process_messages_t44() reads the T44 message which contains the
pending T5 message count. If the number of pending T5 messages returned
by T44 message is too high then there is a risk of i2c transaction
timeout while reading T5 messages in mxt_process_messages_t44().

New property 'atmel,mtu' is created. This property limits the maximum
number of bytes that can read/transferred in an i2c transcation

Signed-off-by: Balasubramani Vivekanandan <balasubramani_vivekanandan@mentor.com>
Signed-off-by: George G. Davis <george_davis@mentor.com>
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
---
drivers/input/touchscreen/atmel_mxt_ts.c | 65 +++++++++++++++++++-----
1 file changed, 51 insertions(+), 14 deletions(-)

diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
index 54cd6219cbaa..384b53717139 100644
--- a/drivers/input/touchscreen/atmel_mxt_ts.c
+++ b/drivers/input/touchscreen/atmel_mxt_ts.c
@@ -417,6 +417,7 @@ struct mxt_data {
/* Indicates whether device is updating configuration */
bool updating_config;

+ unsigned int mtu;
bool t25_status;
};

@@ -1462,11 +1463,32 @@ static int mxt_read_and_process_messages(struct mxt_data *data, u8 count)
return num_valid;
}

+static u8 mxt_max_msg_read_count(struct mxt_data *data, u8 max_T5_msg_count)
+{
+ u8 T5_msg_count_limit = data->mtu / data->T5_msg_size;
+
+ if (!data->mtu)
+ return max_T5_msg_count;
+
+ if (data->mtu < data->T5_msg_size) {
+ WARN(1, "mtu set is lesser than the T5 message size\n");
+ /* Return count of 1, as fallback */
+ return 1;
+ }
+ /*
+ * Return maximum number of T5 messages in single i2c transaction
+ * based on "atmel,mtu" property.
+ */
+ return min(T5_msg_count_limit, max_T5_msg_count);
+}
+
static irqreturn_t mxt_process_messages_t44(struct mxt_data *data)
{
struct device *dev = &data->client->dev;
int ret;
- u8 count, num_left;
+ u8 T5_msg_count, total_pending;
+ u8 total_processed = 0;
+ u8 processed_valid = 0;

/* Read T44 and T5 together */
ret = __mxt_read_reg(data->client, data->T44_address,
@@ -1476,18 +1498,19 @@ static irqreturn_t mxt_process_messages_t44(struct mxt_data *data)
return IRQ_NONE;
}

- count = data->msg_buf[0];
+ T5_msg_count = data->msg_buf[0];

/*
* This condition may be caused by the CHG line being configured in
* Mode 0. It results in unnecessary I2C operations but it is benign.
*/
- if (count == 0)
+ if (!T5_msg_count)
return IRQ_NONE;

- if (count > data->max_reportid) {
- dev_warn(dev, "T44 count %d exceeded max report id\n", count);
- count = data->max_reportid;
+ if (T5_msg_count > data->max_reportid) {
+ dev_warn(dev, "T44 count %d exceeded max report id\n",
+ T5_msg_count);
+ T5_msg_count = data->max_reportid;
}

/* Process first message */
@@ -1497,16 +1520,25 @@ static irqreturn_t mxt_process_messages_t44(struct mxt_data *data)
return IRQ_NONE;
}

- num_left = count - 1;
+ total_pending = T5_msg_count - 1;
+ if (!total_pending)
+ goto end;

/* Process remaining messages if necessary */
- if (num_left) {
- ret = mxt_read_and_process_messages(data, num_left);
+ T5_msg_count = mxt_max_msg_read_count(data, total_pending);
+
+ do {
+ if ((total_pending - total_processed) < T5_msg_count)
+ T5_msg_count = total_pending - total_processed;
+ ret = mxt_read_and_process_messages(data, T5_msg_count);
if (ret < 0)
goto end;
- else if (ret != num_left)
- dev_warn(dev, "Unexpected invalid message\n");
- }
+ total_processed += T5_msg_count;
+ processed_valid += ret;
+ } while (total_processed < total_pending);
+
+ if (processed_valid != total_pending)
+ dev_warn(dev, "Unexpected invalid message\n");

end:
if (data->update_input) {
@@ -1521,9 +1553,10 @@ static int mxt_process_messages_until_invalid(struct mxt_data *data)
{
struct device *dev = &data->client->dev;
int count, read;
- u8 tries = 2;
+ int tries;

- count = data->max_reportid;
+ count = mxt_max_msg_read_count(data, data->max_reportid);
+ tries = (data->max_reportid / count) + 1;

/* Read messages until we force an invalid */
do {
@@ -4120,6 +4153,10 @@ static int mxt_parse_device_properties(struct mxt_data *data)

device_property_read_u32(dev, "atmel,suspend-mode",
&data->suspend_mode);
+ device_property_read_u32(dev, "atmel,mtu", &data->mtu);
+ if (data->mtu)
+ dev_dbg(dev, "mtu is set as %d\n", data->mtu);
+
return 0;
}

--
2.17.1
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