Received-SPF: pass (google.com: domain of linux-kernel+bounces-159797-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Precedence: bulk
MIME-Version: 1.0
References: <20240416182005.75422-1-quic_ajipan@quicinc.com>
 <20240416182005.75422-8-quic_ajipan@quicinc.com> <CAA8EJpqwrKcgm7c57=LpxS7+CfrN2UxNg8k_46auBrdZG7vQnA@mail.gmail.com>
 <ca017ebf-c099-b436-f062-1341f765a08c@quicinc.com>
In-Reply-To: <ca017ebf-c099-b436-f062-1341f765a08c@quicinc.com>
From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date: Fri, 26 Apr 2024 12:35:48 +0300
Message-ID: <CAA8EJporZFsjagW5CU5AwtqDsEXTtGJmRmLRedyBTZa7249p6w@mail.gmail.com>
Subject: Re: [PATCH V2 7/8] clk: qcom: Add GPUCC driver support for SM4450
To: Ajit Pandey <quic_ajipan@quicinc.com>
Cc: Michael Turquette <mturquette@baylibre.com>, Stephen Boyd <sboyd@kernel.org>, 
	Rob Herring <robh@kernel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, 
	Conor Dooley <conor+dt@kernel.org>, Bjorn Andersson <andersson@kernel.org>, 
	Konrad Dybcio <konrad.dybcio@linaro.org>, Vinod Koul <vkoul@kernel.org>, 
	Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>, linux-arm-msm@vger.kernel.org, 
	linux-clk@vger.kernel.org, devicetree@vger.kernel.org, 
	linux-kernel@vger.kernel.org, Taniya Das <quic_tdas@quicinc.com>, 
	Jagadeesh Kona <quic_jkona@quicinc.com>, Imran Shaik <quic_imrashai@quicinc.com>, 
	Satya Priya Kakitapalli <quic_skakitap@quicinc.com>
Content-Type: text/plain; charset="UTF-8"

On Fri, 26 Apr 2024 at 12:20, Ajit Pandey <quic_ajipan@quicinc.com> wrote:
>
>
>
> On 4/17/2024 11:35 AM, Dmitry Baryshkov wrote:
> > On Tue, 16 Apr 2024 at 21:23, Ajit Pandey <quic_ajipan@quicinc.com> wrote:
> >>
> >> Add Graphics Clock Controller (GPUCC) support for SM4450 platform.
> >>
> >> Signed-off-by: Ajit Pandey <quic_ajipan@quicinc.com>
> >> ---
> >>   drivers/clk/qcom/Kconfig        |   9 +
> >>   drivers/clk/qcom/Makefile       |   1 +
> >>   drivers/clk/qcom/gpucc-sm4450.c | 805 ++++++++++++++++++++++++++++++++
> >>   3 files changed, 815 insertions(+)
> >>   create mode 100644 drivers/clk/qcom/gpucc-sm4450.c
> >
> > [skipped]
> >
> >> +
> >> +static int gpu_cc_sm4450_probe(struct platform_device *pdev)
> >> +{
> >> +       struct regmap *regmap;
> >> +
> >> +       regmap = qcom_cc_map(pdev, &gpu_cc_sm4450_desc);
> >> +       if (IS_ERR(regmap))
> >> +               return PTR_ERR(regmap);
> >> +
> >> +       clk_lucid_evo_pll_configure(&gpu_cc_pll0, regmap, &gpu_cc_pll0_config);
> >> +       clk_lucid_evo_pll_configure(&gpu_cc_pll1, regmap, &gpu_cc_pll1_config);
> >> +
> >> +       /* Keep some clocks always enabled */
> >> +       qcom_branch_set_clk_en(regmap, 0x93a4); /* GPU_CC_CB_CLK */
> >> +       qcom_branch_set_clk_en(regmap, 0x9004); /* GPU_CC_CXO_AON_CLK */
> >> +       qcom_branch_set_clk_en(regmap, 0x900c); /* GPU_CC_DEMET_CLK */
> >
> > My main concern here is the AON clocks. If we don't model
> > gpu_cc_demet_clk as a leaf clock, then gpu_cc_demet_div_clk_src
> > becomes a clock without children and can be disabled by Linux.
> > Likewise not modelling gpu_cc_cxo_aon_clk removes one of the voters on
> > gpu_cc_xo_clk_src, which can now be turned off by Linux.
> > Our usual recommendation is to model such clocks properly and to use
> > CLK_IS_CRITICAL or CLK_IGNORE_UNUSED to mark then as aon.
> >
> Thanks for review, actually if leaf (branch) clock is ON, hardware will
> take care of enabling and keeping the parent ON. So parent clocks won't
> get turned OFF in HW as long as branch clock is enabled.
>
> For clocks which are fixed rate (19.2MHz) and recommended to be kept ON
> forever from HW design, modelling and exposing clock structure in kernel
> will be a redundant code in kernel memory, hence as per earlier
> suggestion in previous thread such clocks are recommended to be kept
> enabled from probe.

Recommended by whom?

Kernel developers clearly recommend describing all the clocks so that
CCF has knowledge about all the clocks in the system.

> >> +
> >> +       return qcom_cc_really_probe(pdev, &gpu_cc_sm4450_desc, regmap);
> >> +}
> >> +
> >> +static struct platform_driver gpu_cc_sm4450_driver = {
> >> +       .probe = gpu_cc_sm4450_probe,
> >> +       .driver = {
> >> +               .name = "gpucc-sm4450",
> >> +               .of_match_table = gpu_cc_sm4450_match_table,
> >> +       },
> >> +};
> >> +
> >> +module_platform_driver(gpu_cc_sm4450_driver);
> >> +
> >> +MODULE_DESCRIPTION("QTI GPUCC SM4450 Driver");
> >> +MODULE_LICENSE("GPL");
> >> --
> >> 2.25.1
> >>
> >>
> >
> >
>
> --
> Thanks, and Regards
> Ajit


-- 
With best wishes
Dmitry