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

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Message-ID: <20210301115441.a4s5xzwm6d6ohz7f@vireshk-i7>
Date:   Mon, 1 Mar 2021 17:24:41 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Jie Deng <jie.deng@...el.com>
Cc:     linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, wsa@...nel.org,
        jasowang@...hat.com, wsa+renesas@...g-engineering.com,
        andriy.shevchenko@...ux.intel.com, conghui.chen@...el.com,
        arnd@...db.de, kblaiech@...lanox.com,
        jarkko.nikula@...ux.intel.com, Sergey.Semin@...kalelectronics.ru,
        rppt@...nel.org, loic.poulain@...aro.org, tali.perry1@...il.com,
        u.kleine-koenig@...gutronix.de, bjorn.andersson@...aro.org,
        yu1.wang@...el.com, shuo.a.liu@...el.com
Subject: Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver

On 01-03-21, 14:41, Jie Deng wrote:
> +/**
> + * 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;
> +};

I am not able to appreciate the use of write/read bufs here as we
aren't trying to read/write data in the same transaction. Why do we
have two bufs here as well as in specs ?

What about this on top of your patch ?

---
 drivers/i2c/busses/i2c-virtio.c | 31 +++++++++++--------------------
 include/uapi/linux/virtio_i2c.h |  3 +--
 2 files changed, 12 insertions(+), 22 deletions(-)

diff --git a/drivers/i2c/busses/i2c-virtio.c b/drivers/i2c/busses/i2c-virtio.c
index 8c8bc9545418..e71ab1d2c83f 100644
--- a/drivers/i2c/busses/i2c-virtio.c
+++ b/drivers/i2c/busses/i2c-virtio.c
@@ -67,14 +67,13 @@ static int virtio_i2c_send_reqs(struct virtqueue *vq,
 		if (!buf)
 			break;
 
+		reqs[i].buf = buf;
+		sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
+
 		if (msgs[i].flags & I2C_M_RD) {
-			reqs[i].read_buf = buf;
-			sg_init_one(&msg_buf, reqs[i].read_buf, msgs[i].len);
 			sgs[outcnt + incnt++] = &msg_buf;
 		} else {
-			reqs[i].write_buf = buf;
-			memcpy(reqs[i].write_buf, msgs[i].buf, msgs[i].len);
-			sg_init_one(&msg_buf, reqs[i].write_buf, msgs[i].len);
+			memcpy(reqs[i].buf, msgs[i].buf, msgs[i].len);
 			sgs[outcnt++] = &msg_buf;
 		}
 
@@ -84,13 +83,8 @@ static int virtio_i2c_send_reqs(struct virtqueue *vq,
 		err = virtqueue_add_sgs(vq, sgs, outcnt, incnt, &reqs[i], GFP_KERNEL);
 		if (err < 0) {
 			pr_err("failed to add msg[%d] to virtqueue.\n", i);
-			if (msgs[i].flags & I2C_M_RD) {
-				kfree(reqs[i].read_buf);
-				reqs[i].read_buf = NULL;
-			} else {
-				kfree(reqs[i].write_buf);
-				reqs[i].write_buf = NULL;
-			}
+			kfree(reqs[i].buf);
+			reqs[i].buf = NULL;
 			break;
 		}
 	}
@@ -118,14 +112,11 @@ static int virtio_i2c_complete_reqs(struct virtqueue *vq,
 			break;
 		}
 
-		if (msgs[i].flags & I2C_M_RD) {
-			memcpy(msgs[i].buf, req->read_buf, msgs[i].len);
-			kfree(req->read_buf);
-			req->read_buf = NULL;
-		} else {
-			kfree(req->write_buf);
-			req->write_buf = NULL;
-		}
+		if (msgs[i].flags & I2C_M_RD)
+			memcpy(msgs[i].buf, req->buf, msgs[i].len);
+
+		kfree(req->buf);
+		req->buf = NULL;
 	}
 
 	return i;
diff --git a/include/uapi/linux/virtio_i2c.h b/include/uapi/linux/virtio_i2c.h
index 92febf0c527e..61f0086ac75b 100644
--- a/include/uapi/linux/virtio_i2c.h
+++ b/include/uapi/linux/virtio_i2c.h
@@ -48,8 +48,7 @@ struct virtio_i2c_in_hdr {
  */
 struct virtio_i2c_req {
 	struct virtio_i2c_out_hdr out_hdr;
-	u8 *write_buf;
-	u8 *read_buf;
+	u8 *buf;
 	struct virtio_i2c_in_hdr in_hdr;
 };
 
-- 
viresh