Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver

On 2021/3/2 12:22, Viresh Kumar wrote:

On 02-03-21, 09:31, Viresh Kumar wrote:

quoted

On 01-03-21, 16:19, Arnd Bergmann wrote:

quoted

On Mon, Mar 1, 2021 at 7:41 AM Jie Deng [off-list ref] wrote:

quoted

--- /dev/null
+++ b/include/uapi/linux/virtio_i2c.h

@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later WITH Linux-syscall-note */
+/*
+ * Definitions for virtio I2C Adpter
+ *
+ * Copyright (c) 2021 Intel Corporation. All rights reserved.
+ */
+
+#ifndef _UAPI_LINUX_VIRTIO_I2C_H
+#define _UAPI_LINUX_VIRTIO_I2C_H

Why is this a uapi header? Can't this all be moved into the driver
itself?

quoted

+/**
+ * struct virtio_i2c_req - the virtio I2C request structure
+ * @out_hdr: the OUT header of the virtio I2C message
+ * @write_buf: contains one I2C segment being written to the device
+ * @read_buf: contains one I2C segment being read from the device
+ * @in_hdr: the IN header of the virtio I2C message
+ */
+struct virtio_i2c_req {
+       struct virtio_i2c_out_hdr out_hdr;
+       u8 *write_buf;
+       u8 *read_buf;
+       struct virtio_i2c_in_hdr in_hdr;
+};

In particular, this structure looks like it is only ever usable between
the transfer functions in the driver itself, it is shared with neither
user space nor the virtio host side.

Why is it so ? Won't you expect hypervisors or userspace apps to use
these ?

This comment applies only for the first two structures as the third
one is never exchanged over virtio.

Yeah. Actually, the backend only needs "struct virtio_i2c_out_hdr out_hdr"
and "struct virtio_i2c_in_hdr in_hdr" for communication. So we only need 
to keep
the first two in uapi and move "struct virtio_i2c_req" into the driver.

But Jason wanted to include "struct virtio_i2c_req" in uapi. He 
explained in this link
https://lists.linuxfoundation.org/pipermail/virtualization/2020-October/050222.html.
Do you agree with that explanation ?
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