From: harigovi@codeaurora.org
To: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Cc: "open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
MSM <linux-arm-msm@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>,
DTML <devicetree@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Rob Clark <robdclark@gmail.com>,
nganji@codeaurora.org, Sean Paul <seanpaul@chromium.org>,
kalyan_t@codeaurora.org,
"Kristian H. Kristensen" <hoegsberg@chromium.org>
Subject: Re: [Freedreno] [v1] drm/msm/dsi/pll: call vco set rate explicitly
Date: Tue, 11 Feb 2020 11:28:12 +0530 [thread overview]
Message-ID: <1d201377996e16ce25acb640867e1214@codeaurora.org> (raw)
In-Reply-To: <CAOCk7NoCH9p9gOd7as=ty-EMeerAAhQtKZa8f2wZrDeV2LtGrw@mail.gmail.com>
On 2020-02-07 19:40, Jeffrey Hugo wrote:
> On Fri, Feb 7, 2020 at 5:38 AM <harigovi@codeaurora.org> wrote:
>>
>> On 2020-02-06 20:29, Jeffrey Hugo wrote:
>> > On Thu, Feb 6, 2020 at 2:13 AM Harigovindan P <harigovi@codeaurora.org>
>> > 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
next prev parent reply other threads:[~2020-02-11 5:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-06 9:12 [v1] drm/msm/dsi/pll: call vco set rate explicitly Harigovindan P
2020-02-06 14:59 ` [Freedreno] " Jeffrey Hugo
2020-02-07 12:38 ` harigovi
2020-02-07 14:10 ` Jeffrey Hugo
2020-02-11 5:58 ` harigovi [this message]
2020-02-11 15:44 ` Rob Clark
2020-02-11 15:59 ` Jeffrey Hugo
2020-02-12 0:28 ` Rob Clark
2020-02-12 4:05 ` Jeffrey Hugo
2020-02-12 5:10 ` Rob Clark
2020-02-17 10:42 ` harigovi
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