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

Honza Petrouš
2017-09-15T08:28:12Z

2017-09-14 22:50 GMT+02:00 Mauro Carvalho Chehab <mchehab@s-opensource.com>:
> 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.

Do you mean in stv6110_set_frequency()?

I must say I was shocked by the beginning of it.
Can somebody explain me the reason for such strange
srate computation?

See the head of function:

static int stv6110_set_frequency(struct dvb_frontend *fe, u32 frequency)
{
struct stv6110_priv *priv = fe->tuner_priv;
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
u8 ret = 0x04;
u32 divider, ref, p, presc, i, result_freq, vco_freq;
s32 p_calc, p_calc_opt = 1000, r_div, r_div_opt = 0, p_val;
s32 srate;

dprintk("%s, freq=%d kHz, mclk=%d Hz\n", __func__,
frequency, priv->mclk);

/* K = (Reference / 1000000) - 16 */
priv->regs[RSTV6110_CTRL1] &= ~(0x1f << 3);
priv->regs[RSTV6110_CTRL1] |=
((((priv->mclk / 1000000) - 16) & 0x1f) << 3);

/* BB_GAIN = db/2 */
if (fe->ops.set_property && fe->ops.get_property) {
srate = c->symbol_rate;
dprintk("%s: Get Frontend parameters: srate=%d\n",
__func__, srate);
} else
srate = 15000000;

^^^^ here I would like to note, there there is NO MORE
anything dependant on srate. It looks like some dead code for me.

And the condition sentence looks even more funny - is it
for real to check of retrieval of srate only in case
if some other function pointers are not null?

/Honza

PS: Don't forget that we have duplicated drivers for STV6110,
stv6110 by Igor and stv6110x by Manu.