Re: [PATCH v2 3/6] net: mhi_net: Hold runtime PM during active data path operations

[Paolo Abeni <pabeni@redhat.com>]

On 5/22/26 10:09 PM, Loic Poulain wrote:
> On Fri, May 22, 2026 at 12:01 PM Krishna Chaitanya Chundru
> <krishna.chundru@oss.qualcomm.com> wrote:
>>
>> The mhi_net driver does not coordinate with runtime PM, which allows the
>> underlying MHI controller to be runtime-suspended while transmit, receive,
>> or RX buffer refill operations are in progress. This can lead to stalled
>> transfers or failed queueing once runtime PM is enabled in the MHI core.
>>
>> Add runtime PM reference counting to the mhi_net data path to keep the
>> controller active for the duration of TX, RX, and buffer management
>> operations. Enable runtime PM during probe and take/release references
>> explicitly around these critical paths.
>>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
>> ---
>>  drivers/net/mhi_net.c | 39 +++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 39 insertions(+)
>>
>> diff --git a/drivers/net/mhi_net.c b/drivers/net/mhi_net.c
>> index ae169929a9d8..5d7f9ccdb17b 100644
>> --- a/drivers/net/mhi_net.c
>> +++ b/drivers/net/mhi_net.c
>> @@ -9,6 +9,7 @@
>>  #include <linux/mod_devicetable.h>
>>  #include <linux/module.h>
>>  #include <linux/netdevice.h>
>> +#include <linux/pm_runtime.h>
>>  #include <linux/skbuff.h>
>>  #include <linux/u64_stats_sync.h>
>>
>> @@ -76,11 +77,19 @@ static netdev_tx_t mhi_ndo_xmit(struct sk_buff *skb, struct net_device *ndev)
>>         struct mhi_device *mdev = mhi_netdev->mdev;
>>         int err;
>>
>> +       err = pm_runtime_get(&mdev->dev);
>> +       if (err < 0 && err != -EINPROGRESS) {
>> +               dev_err(&mdev->dev, "pm_runtime_get failed %d\n", err);
>> +               pm_runtime_put_noidle(&mdev->dev);
>> +               goto exit_drop;
>> +       }
>> +
> 
> I am wondering what the value is in pushing this PM responsibility to
> each individual MHI client driver and requiring every MHI operation to
> be bracketed with runtime PM handling.
> 
> What does the client driver know here that the MHI core itself cannot
> handle centrally? It feels like ensuring the controller is
> runtime-active during transfer could be handled generically in the
> framework instead of duplicating the same logic in every client.

Indeed if *feel* like the MHI core should be able to put together all
the status needed to correctly track the PM.

Adding PM tracking to the NIC driver network data-path looks quite bad.

/P