Re: [PATCH 3/9] w1: ds2482: set the strong pull-up with its byte

[Krzysztof Kozlowski]

On 27/10/2026 17:04, Greg Kroah-Hartman wrote:
> From: Josef Bacik <josef@xxxxxxxxxxxxxx>
> 
> The eight channels of a DS2482-800 are eight independent 1-wire masters
> for the w1 core, but share one I2C device. Each bus operation consists of
> several I2C transfers: select the channel, send the command, poll the
> status, set the read pointer, read the result. access_lock keeps the
> operations of the channels apart.
> 
> ds2482_w1_set_pullup() polls the status, writes the configuration and
> polls again without the lock. Polling sets the read pointer of the device
> to the status register. In the middle of a read on another channel, after
> that one has set the pointer to the data register, this makes the read
> return the status instead of the data. The cached copy of the pointer in
> pdev->read_prt can go wrong as well.
> 
> The lock alone is not enough. The strong pull-up is a setting of the
> whole chip which is used up by the next byte. If an operation of another
> channel gets in before the byte it was meant for, that channel gets the
> pull-up, and the sensor converts without power.
> 
> So only note the request in ds2482_w1_set_pullup(), and write the
> configuration in ds2482_w1_write_byte(), under the lock and after the
> channel has been selected. The w1 core calls the former right before the
> latter, under the bus mutex of the channel.
> 
> Fixes: 9c95bb6f25ff ("w1: ds2482: Added 1-Wire pull-up support to the driver")
> Cc: stable <stable@xxxxxxxxxx>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxxxxx>

Best regards,
Krzysztof