Re: [RFC] [DVB][FRONTEND] Added a new ioctl for optimizing frontend property set operation

Mauro Carvalho Chehab
2017-09-14T20:51:15Z

Hi Satendra,

Em Thu, 14 Sep 2017 05:59:27 -0400
Satendra Singh Thakur <satendra.t@samsung.com> escreveu:

> -For setting one frontend property , one FE_SET_PROPERTY ioctl is called
> -Since, size of struct dtv_property is 72 bytes, this ioctl requires
> ---allocating 72 bytes of memory in user space
> ---allocating 72 bytes of memory in kernel space
> ---copying 72 bytes of data from user space to kernel space
> -However, for all the properties, only 8 out of 72 bytes are used
> for setting the property

That's true. Yet, for get, the size can be bigger, as ISDB-T can
return statistics per layer, plus a global one.

> -Four bytes are needed for specifying property type and another 4 for
> property value
> -Moreover, there are 2 properties DTV_CLEAR and DTV_TUNE which use
> only 4 bytes for property name
> ---They don't use property value
> -Therefore, we have defined new short variant/forms/version of currently
> used structures for such 8 byte properties.
> -This results in 89% (8*100/72) of memory saving in user and kernel space
> each.
> -This also results in faster copy (8 bytes as compared to 72 bytes) from
> user to kernel space
> -We have added new ioctl FE_SET_PROPERTY_SHORT which utilizes above
> mentioned new property structures
> -This ioctl can co-exist with present ioctl FE_SET_PROPERTY
> -If the apps wish to use shorter forms they can use
> proposed FE_SET_PROPERTY_SHORT, rest of them can continue to use
> current versions FE_SET_PROPERTY

> -We are currently not validating incoming properties in
> function dtv_property_short_process_set because most of
> the frontend drivers in linux source are not using the
> method ops.set_property. Just two drivers are using it
> drivers/media/dvb-frontends/stv0288.c
> driver/media/usb/dvb-usb/friio-fe.c
> -Moreover, stv0288 driver implemments blank function
> for set_property.
> -If needed in future, we can define a new
> ops.set_property_short method to support
> struct dtv_property_short.

Nah. Better to just get rid of get_property()/set_froperty() for good.

Just sent a RFC patch series doing that.

The only thing is that stv6110 seems to have a dirty hack that may
depend on that. Someone need to double-check if the patch series
I just sent doesn't break anything. If it breaks, then we'll need
to add an extra parameter to stv6110 attach for it to know what
behavior is needed there.

> Signed-off-by: Satendra Singh Thakur <satendra.t@samsung.com>
> ---
> drivers/media/dvb-core/dvb_frontend.c | 228 +++++++++++++++++++++++++++++++++-
> include/uapi/linux/dvb/frontend.h | 24 ++++
> 2 files changed, 248 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
> index e3fff8f..e183025 100644
> --- a/drivers/media/dvb-core/dvb_frontend.c
> +++ b/drivers/media/dvb-core/dvb_frontend.c
> @@ -1914,6 +1914,192 @@ static int dtv_property_process_set(struct dvb_frontend *fe,
> return r;
> }
>
> +/**
> + * dtv_property_short_process_set
> + * @fe: Pointer to struct dvb_frontend
> + * @tvp: Pointer to struct dtv_property_short
> + * @file: Pointer to struct file
> + *
> + * helper function for dvb_frontend_ioctl_properties,
> + * which can be used to set dtv property using ioctl
> + * cmd FE_SET_PROPERTY_SHORT.
> + * It assigns property value to corresponding member of
> + * property-cache structure
> + * This func is a variant of the func dtv_property_process_set
> + * Returns:
> + * Zero on success, negative errno on failure.
> + */
> +static int dtv_property_short_process_set(struct dvb_frontend *fe,
> + struct dtv_property_short *tvp,
> + struct file *file)
> +{
> + int r = 0;
> + struct dtv_frontend_properties *c = &fe->dtv_property_cache;
> + /* Currently, We do not allow the frontend to validate incoming
> + * properties, currently, just 2 drivers are using
> + * ops.set_property method , If required, we can define new
> + * ops.set_property_short method for this purpose
> + */
> + switch (tvp->cmd) {
> + case DTV_CLEAR:

Nah. Let's not have multiple validation routines for each variant.

It would be better to change the parameters for dtv_property_process_set
to something like:

static int dtv_property_process_set(struct dvb_frontend *fe,
struct file *file,
u32 cmd, u32 data)

And have just one validation routine that would work for both.

If we end by adding some DTV properties that would require more than
4 bytes, only such properties would be implemented on a different
function.

> static int dvb_frontend_ioctl(struct file *file,
> unsigned int cmd, void *parg)
> {
> @@ -1939,7 +2125,8 @@ static int dvb_frontend_ioctl(struct file *file,
> return -EPERM;
> }
>
> - if ((cmd == FE_SET_PROPERTY) || (cmd == FE_GET_PROPERTY))
> + if ((cmd == FE_SET_PROPERTY) || (cmd == FE_GET_PROPERTY)
> + || (cmd == FE_SET_PROPERTY_SHORT))
> err = dvb_frontend_ioctl_properties(file, cmd, parg);
> else {
> c->state = DTV_UNDEFINED;
> @@ -2026,9 +2213,42 @@ static int dvb_frontend_ioctl_properties(struct file *file,
> err = -EFAULT;
> goto out;
> }
> -
> - } else
> - err = -EOPNOTSUPP;
> + /* New ioctl for optimizing property set
> + */
> + } else if (cmd == FE_SET_PROPERTY_SHORT) {
> + struct dtv_property_short *tvp_short = NULL;
> + struct dtv_properties_short *tvps_short = parg;
> +
> + dev_dbg(fe->dvb->device, "%s: properties.num = %d\n", \
> + __func__, tvps_short->num);
> + dev_dbg(fe->dvb->device, "%s: properties.props = %p\n", \
> + __func__, tvps_short->props);
> + if ((!tvps_short->num) ||
> + (tvps_short->num > DTV_IOCTL_MAX_MSGS))
> + return -EINVAL;
> + tvp_short = memdup_user(tvps_short->props,
> + tvps_short->num * sizeof(*tvp_short));
> + if (IS_ERR(tvp_short))
> + return PTR_ERR(tvp_short);
> + for (i = 0; i < tvps_short->num; i++) {
> + err = dtv_property_short_process_set(fe, tvp_short + i,\
> + file);
> + if (err < 0) {
> + kfree(tvp_short);
> + return err;
> + }
> + /* Since we are returning when error occurs
> + * There is no need to store the result as it
> + * would have been >=0 in case we didn't return
> + * (tvp + i)->result = err;
> + */
> + }
> + if (c->state == DTV_TUNE)
> + dev_dbg(fe->dvb->device, "%s: Property cache\
> + is full, tuning\n", __func__);

Don't break strings on two lines.

> + kfree(tvp_short);

> + } else
> + err = -EOPNOTSUPP;

Indentation here is wrong.

>
> out:
> kfree(tvp);
> diff --git a/include/uapi/linux/dvb/frontend.h b/include/uapi/linux/dvb/frontend.h
> index 00a20cd..aa82179 100644
> --- a/include/uapi/linux/dvb/frontend.h
> +++ b/include/uapi/linux/dvb/frontend.h
> @@ -476,6 +476,17 @@ struct dtv_property {
> int result;
> } __attribute__ ((packed));
>
> +/**
> + * @struct dtv_property_short
> + * A shorter version of struct dtv_property
> + * @cmd: Property type
> + * @data: Property value
> + */
> +struct dtv_property_short {
> + __u32 cmd;
> + __u32 data;
> +};
> +
> /* num of properties cannot exceed DTV_IOCTL_MAX_MSGS per ioctl */
> #define DTV_IOCTL_MAX_MSGS 64
>
> @@ -484,6 +495,18 @@ struct dtv_properties {
> struct dtv_property *props;
> };
>
> +/**
> + * @struct dtv_properties_short
> + * A variant of struct dtv_properties
> + * to support struct dtv_property_short
> + * @num: Number of properties
> + * @props: Pointer to struct dtv_property_short
> + */
> +struct dtv_properties_short {
> + __u32 num;
> + struct dtv_property_short *props;
> +};
> +
> #if defined(__DVB_CORE__) || !defined (__KERNEL__)
>
> /*
> @@ -565,6 +588,7 @@ struct dvb_frontend_event {
>
> #define FE_SET_PROPERTY _IOW('o', 82, struct dtv_properties)
> #define FE_GET_PROPERTY _IOR('o', 83, struct dtv_properties)
> +#define FE_SET_PROPERTY_SHORT _IOW('o', 84, struct dtv_properties_short)
>
> /**
> * When set, this flag will disable any zigzagging or other "normal" tuning

Thanks,
Mauro