[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1911942e-f770-dbff-969c-b98ed69f68ea@linux.vnet.ibm.com>
Date: Mon, 23 Oct 2017 10:23:02 -0500
From: Eddie James <eajames@...ux.vnet.ibm.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: jdelvare@...e.com, linux-hwmon@...r.kernel.org,
linux-kernel@...r.kernel.org, andrew@...id.au,
"Edward A. James" <eajames@...ibm.com>
Subject: Re: drivers (pmbus): ir35221: Set PMBUS_PAGE before reading id and
model
On 10/21/2017 11:10 AM, Guenter Roeck wrote:
> On Thu, Oct 19, 2017 at 03:57:08PM -0500, eajames@...ux.vnet.ibm.com wrote:
>> From: "Edward A. James" <eajames@...ibm.com>
>>
>> The MFR_ID and MFR_MODEL, which are manually read before probing the
>> pmbus core, are only valid for the two pages that the ir35221 has
>> available. Since we don't know the state of the device when we start
>> probing, set the page number first before reading id and model.
>>
> If the device only has two pages, it is highly unlikely that it is possible
> to select another page which is not supported; any attempts to do so should
> result in a command error.
>
> Is this theory or based on an actual problem observed ? If so, it will require
> some additional explanation.
Hi,
Yes, I have observed this with a physical ir35221 device off an i2c bus.
It seems that there are some places in the PMBUS core that manage to set
the page number to 0xFF due to pmbus_set_page being called with page=-1.
pmbus_set_page doesn't check the CML register, so if the i2c op
succeeds, it will be a success. I can also set it to anything with
i2cset tool without error.
I would also like to fix calling pmbus_set_page with -1, and I will send
up a patch if/when I have time. But I felt it makes sense to also ensure
the page is set correctly in the ir35221 driver, since it's an unknown
state at probe time, and this device appears a bit "weird" in that it
doesn't return an error if it's an unsupported page.
Thanks,
Eddie
>
> Thanks,
> Guenter
>
>> Signed-off-by: Edward A. James <eajames@...ibm.com>
>> ---
>> drivers/hwmon/pmbus/ir35221.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/hwmon/pmbus/ir35221.c b/drivers/hwmon/pmbus/ir35221.c
>> index 8b906b4..9a53930 100644
>> --- a/drivers/hwmon/pmbus/ir35221.c
>> +++ b/drivers/hwmon/pmbus/ir35221.c
>> @@ -267,6 +267,12 @@ static int ir35221_probe(struct i2c_client *client,
>> | I2C_FUNC_SMBUS_READ_BLOCK_DATA))
>> return -ENODEV;
>>
>> + ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, 0);
>> + if (ret < 0) {
>> + dev_err(&client->dev, "Failed to set PMBUS_PAGE\n");
>> + return ret;
>> + }
>> +
>> ret = i2c_smbus_read_block_data(client, PMBUS_MFR_ID, buf);
>> if (ret < 0) {
>> dev_err(&client->dev, "Failed to read PMBUS_MFR_ID\n");
Powered by blists - more mailing lists