linux-kernel - Re: [RFC] staging: vt6656: Add formula to the vnt_rf

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Message-ID: <20200420161855.GB3159@ubuntu>
Date:   Mon, 20 Apr 2020 18:18:55 +0200
From:   Oscar Carter <oscar.carter@....com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Oscar Carter <oscar.carter@....com>,
        Forest Bond <forest@...ttletooquiet.net>,
        Malcolm Priestley <tvboxspy@...il.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] staging: vt6656: Add formula to the vnt_rf_addpower
 function

On Wed, Apr 15, 2020 at 06:25:41PM +0200, Oscar Carter wrote:
> On Tue, Apr 14, 2020 at 04:12:14PM +0300, Dan Carpenter wrote:
> > On Mon, Apr 13, 2020 at 04:02:09PM +0200, Oscar Carter wrote:
> > > diff --git a/drivers/staging/vt6656/rf.c b/drivers/staging/vt6656/rf.c
> > > index 4f9aba0f21b0..3b200d7290a5 100644
> > > --- a/drivers/staging/vt6656/rf.c
> > > +++ b/drivers/staging/vt6656/rf.c
> > > @@ -575,28 +575,14 @@ int vnt_rf_setpower(struct vnt_private *priv, u32 rate, u32 channel)
> > >
> > >  static u8 vnt_rf_addpower(struct vnt_private *priv)
> > >  {
> > > +	s32 base;
> >
> > Just use "int".  s32 is for when signed 32 bit is specified in the
> > hardware.  I realize that it's done in this file, but if all your
> > friends jumped off a bridge doesn't mean you should drink their kool-aid.
>
> Ok, lesson learned and thanks for the aclaration about when use every type.
>
> > >  	s32 rssi = -priv->current_rssi;
> > >
> > >  	if (!rssi)
> > >  		return 7;
> > >
> > > -	if (priv->rf_type == RF_VT3226D0) {
> > > -		if (rssi < -70)
> > > -			return 9;
> > > -		else if (rssi < -65)
> > > -			return 7;
> > > -		else if (rssi < -60)
> > > -			return 5;
> > > -	} else {
> > > -		if (rssi < -80)
> > > -			return 9;
> > > -		else if (rssi < -75)
> > > -			return 7;
> > > -		else if (rssi < -70)
> > > -			return 5;
> > > -	}
> > > -
> > > -	return 0;
> > > +	base = (priv->rf_type == RF_VT3226D0) ? -60 : -70;
> > > +	return (rssi < base--) ? ((rssi - base) / -5) * 2 + 5 : 0;
> >                        ^^^^^^
> > I quite hate this postop.  It would have been cleaner to write it like:
> >
> > 	return (rssi < base) ? ((rssi - (base - 1)) / -5) * 2 + 5 : 0
>                                         ^        ^
> Now, if we apply the minus operator one parentheses can be removed. The
> same expression is now:
>
>   	return (rssi < base) ? ((rssi - base + 1) / -5) * 2 + 5 : 0
>
> I think it's clear enought.
>
> > I'm sorry, I'm not clever enough to figure out the potential values of
> > "rssi".
>
> The IEEE 802.11 standard specifies that RSSI can be on a scale of 0 to
> up to 255, and that each chipset manufacturer can define their own max
> RSSI value.  It's all up to the manufacturer.
>
> > How did you work out this formula?  It feels like it came from
> > a standard or something?
>
> I realized that the two branches of the if statement return the same
> values (5, 7, 9) and that each value has a difference of 2 units from
> the previous one. Also, every branch has 3 ranges, and every range has
> an interval of 5. The only difference in this case is the "base" value
> of each branch.
>
> So, the solution was obtain the range index --> (rssi - base) / -5
> Then, we need two units for every range index -> * 2
> Now, the return value starts with five -------> + 5
>
> The base-- was to obtain the range index the same that the orignal
> function.
>
> > Do we not have a function already which implements the standard?
>
> I have been searching but I have not found anything that relates the
> RSSI value with the amount of power to add. I have found
>
> struct station_parameters -> member txpwr (struct sta_txpwr type)
>
> but all the functions related to this doesn't set the tx power
> depending on the RSSI value.
>
I will create a new version with the previous comments (only change the
type of "base" variable to "int"), but what's the correct process for
an RFC patch. I need to send an email with the subject RFC v2 or now I
can send an email with the subject PATCH v2.

> > regards,
> > dan carpenter
> >
>
> thanks,
> oscar carter

thanks,
oscar carter