Hi Marek,
On Sat, Jun 13, 2020 at 04:56:32PM +0200, Marek Vasut wrote:
> Some I2C controllers have a hard limit on the number of data they can
> transfer in one transfer (e.g. Xilinx XIIC has 255 bytes). The Atmel
> MXT touchscreen driver mxt_process_messages_until_invalid() function
> can trigger a read much longer than that (e.g. 690 bytes in my case).
> This transfer can however be easily split into multiple shorter ones,
> esp. since the single T5 message is 10 bytes or so.
>
> This patch adds a check for the quirk presence and if it is present,
> limits the number of messages read out of the controller such that
> they are below the quirk limit. This makes it possible for the MXT
> driver to work even on such limited controllers.
>
> Signed-off-by: Marek Vasut <marex@xxxxxxx>
> Cc: Nick Dyer <nick@xxxxxxxxxxxxx>
> Cc: Evan Green <evgreen@xxxxxxxxxxxx>
> Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> Cc: Sasha Levin <sashal@xxxxxxxxxx>
> ---
> drivers/input/touchscreen/atmel_mxt_ts.c | 30 ++++++++++++++++++------
> 1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> index a2189739e30f5..faa3f3f987d46 100644
> --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> @@ -985,21 +985,37 @@ static int mxt_proc_message(struct mxt_data *data, u8 *message)
>
> static int mxt_read_and_process_messages(struct mxt_data *data, u8 count)
> {
> + const struct i2c_adapter_quirks *q = data->client->adapter->quirks;
> struct device *dev = &data->client->dev;
> - int ret;
> - int i;
> + int i, ret, offset = 0;
> + u16 rem, chunk = count, total = count;
> u8 num_valid = 0;
>
> /* Safety check for msg_buf */
> if (count > data->max_reportid)
> return -EINVAL;
>
> + /* Handle controller read-length limitations */
> + if (q && q->max_read_len) {
> + chunk = min((u16)(q->max_read_len / data->T5_msg_size),
> + (u16)count);
I do not think you need this min() here. The "rem = min(total, chunk);"
below will take care of cases where chunk is bigger than total count.
> + }
> +
> /* Process remaining messages if necessary */
> - ret = __mxt_read_reg(data->client, data->T5_address,
> - data->T5_msg_size * count, data->msg_buf);
> - if (ret) {
> - dev_err(dev, "Failed to read %u messages (%d)\n", count, ret);
> - return ret;
> + while (total) {
> + rem = min(total, chunk);
> + ret = __mxt_read_reg(data->client, data->T5_address,
> + data->T5_msg_size * rem,
> + data->msg_buf +
> + (offset * data->T5_msg_size));
> + if (ret) {
> + dev_err(dev,
> + "Failed to read %u messages (offset %u of total %u) (%d)\n",
> + rem, offset, count, ret);
> + return ret;
> + }
> + total -= rem;
> + offset += rem;
> }
>
> for (i = 0; i < count; i++) {
> --
> 2.26.2
>
Thanks.
--
Dmitry
