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SubjectRe: RE: RE: [PATCH v2 1/2] clk: divider: prepare for minimum divider
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Quoting Mohammed, Afzal (2013-01-25 04:06:41)
> Hi Mike,
>
> On Thu, Jan 24, 2013 at 22:36:30, Mike Turquette wrote:
> > Quoting Mohammed, Afzal (2013-01-24 03:29:15)
>
> > > It is a functional constraint: divider has 8 bits and it can have
> > > all possible values (0 to 255) and divider value corresponds to
> > > value set in the 8 bits. But depending on the modes the minimum
> > > value that can be configured (to get display working) varies.
> > > Eg. For raster mode (which the driver is presently supporting), it
> > > can take a minimum value of 2, while in LIDD (LCD interface display
> > > driver) mode it can take a min value of 1.
> > >
> > > Here min rate is not a constraint w.r.t divider in LCDC IP, but
> > > rather min divider.
>
> > Just so I understand correctly... you are saying that the functional
> > constraint is not caused by the clock rate, but instead by the divider
> > value? For the different modes (raster vs LIDD) is the clock rate the
> > same, or is the clock rate different?
>
> > What is the clock output rate of the divider in raster mode? What is
> > the clock output rate of the divider in LIDD mode?
>
> Yes, functional constraint in caused by divider value.
>
> clock output rate can defined for both modes as follows,
>
> p_clk (clock output rate) = lcd_clk (input clock rate) / div,
>
> to configure "div", we have r/w 8 bits, so div values can
> range from 0-255,
>
> And IP spec says value "0" and "1" should not be written, in
> raster mode. Further it says if in LIDD mode it can have values
> from 0-255, but effect of writing "0" is same as "1".
>

Afzal,

Thank you for the information. In short, the way you program your clock
depend on the configuration of your lcdc device.

As such I am not sure the basic divider is the right choice for you.
You might be better off creating a clock for your IP which takes into
account these details. Luckily it is possible to inherit from the basic
clock types and create a new type.

An example of this is the MXS divider. It uses the basic divider as a
"parent class" and adds a busy bit. This is a better approach than
putting every feature into the basic divider type. You can see how it
was done in drivers/clk/mxs/clk-div.c

Let me know what you think.

Regards,
Mike

> Effect of divider value on output rate is in the same way for
> both modes as per above expression (except for writing "0" in
> LIDD mode).
>
> The driver supports only raster mode.
>
> Regards
> Afzal
>
> Note: link to trm has been mentioned in the earlier reply.


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