Messages in this thread Patch in this message | | | From | Felix Knopf <> | Subject | Re: [PATCH] driver: adc: ltc2497: return directly after reading the adc conversion value | Date | Tue, 25 May 2021 10:22:36 +0200 |
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>> On Wed, May 12, 2021 at 12:57:25PM +0800, Meng.Li@windriver.com wrote: >>> When read adc conversion value with below command: >>> cat /sys/.../iio:device0/in_voltage0-voltage1_raw >>> There is an error reported as below: >>> ltc2497 0-0014: i2c transfer failed: -EREMOTEIO This i2c transfer >>> issue is introduced by commit 69548b7c2c4f ("iio: >>> adc: ltc2497: split protocol independent part in a separate module"). >>> When extract the common code into ltc2497-core.c, it change the code >>> logic of function ltc2497core_read(). With wrong reading sequence, the >>> action of enable adc channel is sent to chip again during adc channel >>> is in conversion status. In this way, there is no ack from chip, and >>> then cause i2c transfer failed.
Hi,
I came across the same or a very similar issue with the ltc2497 but took a different approach to solve it. I suspect this issue is caused by a suboptimal I2C access pattern.
The ltc2497 triggers a new conversion on the stop condition of transactions addressed to it. As the chip cannot communicate during a conversion, it will not ACK until it is finished. The current driver produces the following sequence to read from an arbitrary channel:
ltc2497_result_and_measure(…, NULL); 1) S <ADDR> W A | <CONF> A | P (select channel)
2) [sleep 150ms] (wait for conversion)
ltc2497_result_and_measure(…, val); 3) S <ADDR> R A | <data> … | P (read data) 4) S <ADDR> W N | P (chip is busy, error)
Transaction 3 triggers a new conversion on the previously selected channel and causes the following channel select (4) to fail. The examples in the datasheet [1] make use of repeated start conditions to prevent unintended triggers. In our case, 3 and 4 should be combined into one transaction.
Limeng's patch sikps 4 which solves the problem but causes issues at high sample rates, were 1 is skipped by the core.
I attached my ad-hoc solution below. @Limeng: Could you test this with your hardware?
If there is interest, I will prepare a proper patch. (Should that go into a new thread then?)
Regards, Felix
[1] https://www.analog.com/media/en/technical-documentation/data-sheets/2497fb.pdf#page=18
-- Felix Knopf von Hoerner & Sulger GmbH https://vh-s.de
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c index 1adddf5a88a9..8968bf70859b 100644 --- a/drivers/iio/adc/ltc2497.c +++ b/drivers/iio/adc/ltc2497.c @@ -34,20 +34,23 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata, int ret; if (val) { - ret = i2c_master_recv(st->client, (char *)&st->buf, 3); + ret = i2c_smbus_read_i2c_block_data(st->client, + LTC2497_ENABLE | address, 3, + (char *)&st->buf); if (ret < 0) { - dev_err(&st->client->dev, "i2c_master_recv failed\n"); + dev_err(&st->client->dev, "i2c transfer failed\n"); return ret; } *val = (be32_to_cpu(st->buf) >> 14) - (1 << 17); + } else { + ret = i2c_smbus_write_byte(st->client, + LTC2497_ENABLE | address); + if (ret) + dev_err(&st->client->dev, "i2c write failed: %pe\n", + ERR_PTR(ret)); } - ret = i2c_smbus_write_byte(st->client, - LTC2497_ENABLE | address); - if (ret) - dev_err(&st->client->dev, "i2c transfer failed: %pe\n", - ERR_PTR(ret)); return ret; }
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