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SubjectRe: [PATCH 2/2] drivers/misc: add transfer ioctl for HPS
On Thu, Jan 27, 2022 at 07:35:45PM +1100, Sami Kyöstilä wrote:
> This patch adds an ioctl operation for sending and receiving data from
> the ChromeOS snooping protection sensor (a.k.a., HPS). This allows
> userspace programs to perform a combined read/write I2C transaction
> through a single syscall.
>
> The I2C wire protocol for the device is documented at:
>
> https://chromium.googlesource.com/chromiumos/platform/hps-firmware/+/
> refs/heads/main/docs/host_device_i2c_protocol.md
>
> Signed-off-by: Sami Kyöstilä <skyostil@chromium.org>
> ---
>
> MAINTAINERS | 1 +
> drivers/misc/hps-i2c.c | 81 ++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/hps.h | 20 ++++++++++
> 3 files changed, 102 insertions(+)
> create mode 100644 include/uapi/linux/hps.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 9dea4b8c2ab5..d5fc066fdbc2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8803,6 +8803,7 @@ M: Sami Kyöstilä <skyostil@chromium.org>
> R: Evan Benn <evanbenn@chromium.org>
> S: Maintained
> F: drivers/misc/hps-i2c.c
> +F: include/uapi/linux/hps.h
>
> HSI SUBSYSTEM
> M: Sebastian Reichel <sre@kernel.org>
> diff --git a/drivers/misc/hps-i2c.c b/drivers/misc/hps-i2c.c
> index fe9f073b0352..748ead49d678 100644
> --- a/drivers/misc/hps-i2c.c
> +++ b/drivers/misc/hps-i2c.c
> @@ -17,9 +17,11 @@
> #include <linux/i2c.h>
> #include <linux/module.h>
> #include <linux/pm_runtime.h>
> +#include <uapi/linux/hps.h>
>
> #define HPS_ACPI_ID "GOOG0020"
> #define HPS_MAX_DEVICES 1
> +#define HPS_MAX_MSG_SIZE 8192
>
> struct hps_drvdata {
> struct i2c_client *client;
> @@ -60,6 +62,8 @@ static int hps_open(struct inode *inode, struct file *file)
> ret = pm_runtime_get_sync(dev);
> if (ret < 0)
> goto pm_get_fail;
> +
> + file->private_data = hps->client;
> return 0;
>
> pm_get_fail:
> @@ -84,10 +88,87 @@ static int hps_release(struct inode *inode, struct file *file)
> return ret;
> }
>
> +static int hps_do_ioctl_transfer(struct i2c_client *client,
> + struct hps_transfer_ioctl_data *args)
> +{
> + int ret;
> + int nmsg = 0;
> + struct i2c_msg msgs[2] = {
> + {
> + .addr = client->addr,
> + .flags = client->flags,
> + },
> + {
> + .addr = client->addr,
> + .flags = client->flags,
> + },
> + };
> +
> + if (args->isize) {
> + msgs[nmsg].len = args->isize;
> + msgs[nmsg].buf = memdup_user(args->ibuf, args->isize);
> + if (IS_ERR(msgs[nmsg].buf)) {
> + ret = PTR_ERR(msgs[nmsg].buf);
> + goto memdup_fail;
> + }
> + nmsg++;
> + }
> +
> + if (args->osize) {
> + msgs[nmsg].len = args->osize;
> + msgs[nmsg].buf = memdup_user(args->obuf, args->osize);
> + msgs[nmsg].flags |= I2C_M_RD;
> + if (IS_ERR(msgs[nmsg].buf)) {
> + ret = PTR_ERR(msgs[nmsg].buf);
> + goto memdup_fail;
> + }
> + nmsg++;
> + }
> +
> + ret = i2c_transfer(client->adapter, &msgs[0], nmsg);
> + if (ret > 0 && args->osize) {
> + if (copy_to_user(args->obuf, msgs[nmsg - 1].buf, ret))
> + ret = -EFAULT;
> + }

Why can't you just do normal i2c transfers to/from userspace instead of
requring a custom ioctl?

thanks,

greg k-h

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