From: Amit Nischal <anischal@codeaurora.org>
To: Stephen Boyd <sboyd@kernel.org>
Cc: Jordan Crouse <jcrouse@codeaurora.org>,
Michael Turquette <mturquette@baylibre.com>,
Andy Gross <andy.gross@linaro.org>,
David Brown <david.brown@linaro.org>,
Rajendra Nayak <rnayak@codeaurora.org>,
Odelu Kukatla <okukatla@codeaurora.org>,
Taniya Das <tdas@codeaurora.org>,
linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org,
linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-clk-owner@vger.kernel.org
Subject: Re: [PATCH 2/4] clk: qcom: Add clk_rcg2_gfx3d_ops for SDM845
Date: Mon, 13 Aug 2018 12:00:38 +0530 [thread overview]
Message-ID: <f8ccc09afc44c182a1b4add3dea4f437@codeaurora.org> (raw)
In-Reply-To: <153370789988.220756.1656616273823792690@swboyd.mtv.corp.google.com>
On 2018-08-08 11:28, Stephen Boyd wrote:
> Quoting Jordan Crouse (2018-08-06 08:04:37)
>> On Mon, Aug 06, 2018 at 02:37:18PM +0530, Amit Nischal wrote:
>> > On 2018-08-03 04:14, Stephen Boyd wrote:
>> > >Quoting Amit Nischal (2018-07-30 04:28:56)
>> > >>On 2018-07-25 12:28, Stephen Boyd wrote:
>> > >>>
>> > >>> Ok. Sounds good! Is the rate range call really needed? It can't be
>> > >>> determined in the PLL code with some table or avoided by making sure
>> > >>> GPU
>> > >>> uses OPP table with only approved frequencies?
>> > >>>
>> > >>
>> > >>Currently fabia PLL code does not have any table to check this and
>> > >>intention
>> > >>was to avoid relying on the client to call set_rate with only approved
>> > >>frequencies so we have added the set_rate_range() call in the GPUCC
>> > >>driver
>> > >>in order to set the rate range.
>> > >>
>> > >
>> > >But GPU will use OPP so it doesn't seem like it really buys us anything
>> > >here. And it really doesn't matter when the clk driver implementation
>> > >doesn't use the min/max to clamp the values of the round_rate()
>> > >call. Is
>> > >that being done here? I need to double check. I would be more convinced
>> > >if the implementation was looking at min/max to constrain the rate
>> > >requested.
>> > >
>> >
>> > So our understanding is that GPU(client) driver will always call the
>> > set_rate with approved frequencies only and we can completely rely
>> > on the
>> > client. Is our understanding is correct?
>>
>>
>> First: on sdm845 the software doesn't set the GPU clocks - we rely on
>> the GMU
>> firmware to do that on our behalf but for the GPU at least this is an
>> academic
>> exercise.
>
> So what is this GPU clk driver for then?
>
>>
>> But that said: traditionally we've expected that the clock driver
>> correctly
>> clamp the requested rate to the correct values. In the past we have
>> taken
>> advantage of this and we may in the future. I don't think it is
>> reasonable
>> to require the leaf driver to only pass "approved" frequencies
>> especially
>> since we depend on our own OPP table that may or may not be similar to
>> the
>> one used by the clock driver.
>>
>
> Ok. Sounds like things can't be kept in sync between the clk driver and
> the OPP tables. Why is that hard to do?
>
> Either way, I'd be fine if the code actually used the frequency limits
> to round the rate to something within range, but I don't recall seeing
> that being done here. So if the min/max limits stay, the clk driver
> should round to within that range.
>
Thanks Stephen for your suggestion. I have modified the existing
determine_rate() op to use the min/max limits and round the requested
rate so that it stays withing the set_rate range. I will submit the
same in the next patch series.
> --
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next prev parent reply other threads:[~2018-08-13 6:30 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-06 11:41 [PATCH 0/4] Add QCOM graphics clock controller driver for SDM845 Amit Nischal
2018-06-06 11:41 ` [PATCH 1/4] clk: qcom: gdsc: Add support to enable/disable the clocks with GDSC Amit Nischal
2018-07-09 5:34 ` Stephen Boyd
2018-07-12 12:23 ` Amit Nischal
2018-07-25 6:52 ` Stephen Boyd
2018-07-30 11:14 ` Amit Nischal
2018-06-06 11:41 ` [PATCH 2/4] clk: qcom: Add clk_rcg2_gfx3d_ops for SDM845 Amit Nischal
2018-07-09 6:15 ` Stephen Boyd
2018-07-12 12:30 ` Amit Nischal
2018-07-25 6:58 ` Stephen Boyd
2018-07-30 11:28 ` Amit Nischal
2018-08-02 22:44 ` Stephen Boyd
2018-08-06 9:07 ` Amit Nischal
2018-08-06 15:04 ` Jordan Crouse
2018-08-08 5:58 ` Stephen Boyd
2018-08-08 14:51 ` Jordan Crouse
2018-08-13 6:30 ` Amit Nischal [this message]
2018-06-06 11:41 ` [PATCH 3/4] dt-bindings: clock: Introduce QCOM Graphics clock bindings Amit Nischal
2018-07-09 5:38 ` Stephen Boyd
2018-07-12 12:32 ` Amit Nischal
2018-06-06 11:41 ` [PATCH 4/4] clk: qcom: Add graphics clock controller driver for SDM845 Amit Nischal
2018-07-09 6:07 ` Stephen Boyd
2018-07-12 12:38 ` Amit Nischal
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