On 2020-02-07 19:40, Jeffrey Hugo wrote:
On Fri, Feb 7, 2020 at 5:38 AM <harigovi@xxxxxxxxxxxxxx> wrote:
On 2020-02-06 20:29, Jeffrey Hugo wrote:
> On Thu, Feb 6, 2020 at 2:13 AM Harigovindan P <harigovi@xxxxxxxxxxxxxx>
> wrote:
>>
>> For a given byte clock, if VCO recalc value is exactly same as
>> vco set rate value, vco_set_rate does not get called assuming
>> VCO is already set to required value. But Due to GDSC toggle,
>> VCO values are erased in the HW. To make sure VCO is programmed
>> correctly, we forcefully call set_rate from vco_prepare.
>
> Is this specific to certain SoCs? I don't think I've observed this.
As far as Qualcomm SOCs are concerned, since pll is analog and the
value
is directly read from hardware if we get recalc value same as set rate
value, the vco_set_rate will not be invoked. We checked in our idp
device which has the same SOC but it works there since the rates are
different.
This doesn't seem to be an answer to my question. What Qualcomm SoCs
does this issue apply to? Everything implementing the 10nm pll? One
specific SoC? I don't believe I've seen this on MSM8998, nor SDM845,
so I'm interested to know what is the actual impact here. I don't see
an "IDP" SoC in the IP catalog, so I really have no idea what you are
referring to.
This is not 10nm specific. It is applicable for other nms also.
Its specific to the frequency being set. If vco_recalc returns the same
value as being set by vco_set_rate,
vco_set_rate will not be invoked second time onwards.
For example: Lets take below devices:
Cheza is based on SDM845 which is 10nm only.
Clk frequency:206016
dsi_pll_10nm_vco_set_rate - DSI PLL0 rate=1236096000
dsi_pll_10nm_vco_recalc_rate - DSI PLL0 returning vco rate = 1236095947
Trogdor is based on sc7180 which is also 10nm.
Clk frequency:69300
dsi_pll_10nm_vco_set_rate - DSI PLL0 rate=1663200000
dsi_pll_10nm_vco_recalc_rate - DSI PLL0 returning vco rate = 1663200000
In same trogdor device, we slightly changed the clock frequency and the
values actually differ which will not cause any issue.
Clk frequency:69310
dsi_pll_10nm_vco_set_rate - DSI PLL0 rate=1663440000
dsi_pll_10nm_vco_recalc_rate - DSI PLL0 returning vco rate = 1663439941
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