From: Jie Deng <jie.deng@intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Linux I2C" <linux-i2c@vger.kernel.org>,
virtualization@lists.linux-foundation.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
"Wolfram Sang" <wsa@kernel.org>,
"Jason Wang" <jasowang@redhat.com>,
"Wolfram Sang" <wsa+renesas@sang-engineering.com>,
"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
conghui.chen@intel.com, kblaiech@mellanox.com,
jarkko.nikula@linux.intel.com,
"Sergey Semin" <Sergey.Semin@baikalelectronics.ru>,
"Mike Rapoport" <rppt@kernel.org>,
loic.poulain@linaro.org, "Tali Perry" <tali.perry1@gmail.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Bjorn Andersson" <bjorn.andersson@linaro.org>,
yu1.wang@intel.com, shuo.a.liu@intel.com,
"Viresh Kumar" <viresh.kumar@linaro.org>,
"Stefan Hajnoczi" <stefanha@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [PATCH v7] i2c: virtio: add a virtio i2c frontend driver
Date: Mon, 15 Mar 2021 09:14:37 +0800 [thread overview]
Message-ID: <8070f03d-8233-636b-5ea9-395e723f7a2c@intel.com> (raw)
In-Reply-To: <CAK8P3a0zQG3pH91emqAUsaRx4AZeuOEvSrPzXP9w_XhjU6w3ng@mail.gmail.com>
On 2021/3/12 16:58, Arnd Bergmann wrote:
> On Fri, Mar 12, 2021 at 2:33 PM Jie Deng <jie.deng@intel.com> wrote:
>
>> +
>> +/**
>> + * struct virtio_i2c_req - the virtio I2C request structure
>> + * @out_hdr: the OUT header of the virtio I2C message
>> + * @buf: the buffer into which data is read, or from which it's written
>> + * @in_hdr: the IN header of the virtio I2C message
>> + */
>> +struct virtio_i2c_req {
>> + struct virtio_i2c_out_hdr out_hdr;
>> + uint8_t *buf;
>> + struct virtio_i2c_in_hdr in_hdr;
>> +};
> The simpler request structure clearly looks better than the previous version,
> but I think I found another problem here, at least a theoretical one:
>
> When you map the headers into the DMA address space, they should
> be in separate cache lines, to allow the DMA mapping interfaces to
> perform cache management on each one without accidentally clobbering
> another member.
>
> So far I think there is an assumption that virtio buffers are always
> on cache-coherent devices, but if you ever have a virtio-i2c device
> backend on a physical interconnect that is not cache coherent (e.g. a
> microcontroller that shares the memory bus), this breaks down.
>
> You could avoid this by either allocating arrays of each type separately,
> or by marking each member that you pass to the device as
> ____cacheline_aligned.
>
> Arnd
The virtio devices are software emulated. The backend software may need to
consider this since it may exchange data with physical devices. But I
don't think
we need it for this interface, because no DMA operation is involved
between the
frontend driver and backend driver.
Regards,
Jie
next prev parent reply other threads:[~2021-03-15 1:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-12 13:33 [PATCH v7] i2c: virtio: add a virtio i2c frontend driver Jie Deng
2021-03-12 5:53 ` Jie Deng
2021-03-12 6:10 ` Viresh Kumar
2021-03-12 7:51 ` Jie Deng
2021-03-12 8:11 ` Viresh Kumar
2021-03-12 8:37 ` Jie Deng
2021-03-16 7:39 ` Viresh Kumar
2021-03-12 8:58 ` Arnd Bergmann
2021-03-15 1:14 ` Jie Deng [this message]
2021-03-15 3:13 ` Jason Wang
2021-03-15 5:52 ` Jie Deng
2021-03-15 7:52 ` Arnd Bergmann
2021-03-16 2:15 ` Jie Deng
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