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Subject: Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     linux-i2c@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
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        jasowang@redhat.com, wsa+renesas@sang-engineering.com,
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        arnd@arndb.de, kblaiech@mellanox.com,
        jarkko.nikula@linux.intel.com, Sergey.Semin@baikalelectronics.ru,
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        u.kleine-koenig@pengutronix.de, bjorn.andersson@linaro.org,
        yu1.wang@intel.com, shuo.a.liu@intel.com, stefanha@redhat.com,
        pbonzini@redhat.com
References: <cd3b0c9138824b0a5fad9d3bc872d8836e829946.1615554673.git.jie.deng@intel.com>
 <20210312061012.slmfnhxe6y5kgrnv@vireshk-i7>
From:   Jie Deng <jie.deng@intel.com>
Message-ID: <a97c64ea-773a-133b-c37c-cd02493e0230@intel.com>
Date:   Fri, 12 Mar 2021 15:51:13 +0800
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On 2021/3/12 14:10, Viresh Kumar wrote:
> I saw your email about wrong version being sent, I already wrote some
> reviews. Sending them anyway for FWIW :)
>
> On 12-03-21, 21:33, Jie Deng wrote:
>> +struct virtio_i2c {
>> +	struct virtio_device *vdev;
>> +	struct completion completion;
>> +	struct i2c_adapter adap;
>> +	struct mutex lock;
> As I said in the previous version (Yes, we were both waiting for
> Wolfram to answer that), this lock shouldn't be required at all.
>
> And since none of us have a use-case at hand where we will have a
> problem without this lock, we should really skip it. We can always
> come back and add it if we find an issue somewhere. Until then, better
> to keep it simple.
The problem is you can't guarantee that adap->algo->master_xfer
is only called from i2c_transfer. Any function who holds the adapter can 
call
adap->algo->master_xfer directly. I prefer to avoid potential issues 
rather than
find a issue then fix.
>
>> +
>> +static struct i2c_adapter virtio_adapter = {
>> +	.owner = THIS_MODULE,
>> +	.name = "Virtio I2C Adapter",
>> +	.class = I2C_CLASS_DEPRECATED,
> What happened to this discussion ?
>
> https://lore.kernel.org/lkml/20210305072903.wtw645rukmqr5hx5@vireshk-i7/

My understanding is that new driver sets this to warn users that the 
adapter doesn't support classes anymore.

I'm not sure if Wolfram can explain it more clear for you.

>
>> +	.algo = &virtio_algorithm,
>> +
>> +		return ret;
>> +
>> +	vi->adap = virtio_adapter;
> This is strange, why are you allocating memory for adapter twice ?
> Once for virtio_adapter and once for vi->adap ? Either fill the fields
> directly for v->adap here and remove virtio_adapter or make vi->adap a
> pointer.

Will make vi->adap a pointer. Thanks.