linux-kernel - Re: [v2 3/3] drm/mediatek: add mipi

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Date:   Mon, 6 May 2019 17:17:38 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Jitao Shi <jitao.shi@...iatek.com>
CC:     Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Kumar Gala <galak@...eaurora.org>, <linux-pwm@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        Thierry Reding <treding@...dia.com>,
        "Ajay Kumar" <ajaykumar.rs@...sung.com>,
        Inki Dae <inki.dae@...sung.com>,
        "Rahul Sharma" <rahul.sharma@...sung.com>,
        Sean Paul <seanpaul@...omium.org>,
        Vincent Palatin <vpalatin@...omium.org>,
        Andy Yan <andy.yan@...k-chips.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "Russell King" <rmk+kernel@....linux.org.uk>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>,
        Sascha Hauer <kernel@...gutronix.de>,
        <yingjoe.chen@...iatek.com>, <eddie.huang@...iatek.com>,
        <cawa.cheng@...iatek.com>, <bibby.hsieh@...iatek.com>,
        <stonea168@....com>
Subject: Re: [v2 3/3] drm/mediatek: add mipi_tx driver for mt8183

Hi, Jitao:

On Tue, 2019-04-16 at 13:42 +0800, Jitao Shi wrote:
> This patch add mt8183 mipi_tx driver.
> And also support other chips that use the same binding and driver.
> 
> Signed-off-by: Jitao Shi <jitao.shi@...iatek.com>
> ---
>  drivers/gpu/drm/mediatek/Makefile             |   1 +
>  drivers/gpu/drm/mediatek/mtk_mipi_tx.c        |   2 +
>  drivers/gpu/drm/mediatek/mtk_mipi_tx.h        |   1 +
>  drivers/gpu/drm/mediatek/mtk_mt8183_mipi_tx.c | 154 ++++++++++++++++++
>  4 files changed, 158 insertions(+)
>  create mode 100644 drivers/gpu/drm/mediatek/mtk_mt8183_mipi_tx.c
> 

[snip]

> +
> +static int mtk_mipi_tx_pll_prepare(struct clk_hw *hw)
> +{
> +	struct mtk_mipi_tx *mipi_tx = mtk_mipi_tx_from_clk_hw(hw);
> +	unsigned int txdiv, txdiv0;
> +	u64 pcw;
> +	int ret;
> +
> +	dev_dbg(mipi_tx->dev, "prepare: %u bps\n", mipi_tx->data_rate);
> +
> +	if (mipi_tx->data_rate >= 2000000000) {
> +		txdiv = 1;
> +		txdiv0 = 0;
> +	} else if (mipi_tx->data_rate >= 1000000000) {
> +		txdiv = 2;
> +		txdiv0 = 1;
> +	} else if (mipi_tx->data_rate >= 500000000) {
> +		txdiv = 4;
> +		txdiv0 = 2;
> +	} else if (mipi_tx->data_rate > 250000000) {
> +		txdiv = 8;
> +		txdiv0 = 3;
> +	} else if (mipi_tx->data_rate >= 125000000) {
> +		txdiv = 16;
> +		txdiv0 = 4;
> +	} else {
> +		return -EINVAL;
> +	}
> +
> +	ret = clk_prepare_enable(mipi_tx->ref_clk);
> +	if (ret < 0) {
> +		dev_err(mipi_tx->dev,
> +			"can't prepare and enable mipi_tx ref_clk %d\n", ret);
> +		return ret;
> +	}

You enable the parent clock when prepare this clock here, this behavior
looks strange. I think the flow should be:

1. Parent clock prepare
2. This clock prepare
3. Parent clock enable
4. This clock enable

Maybe you should implement 'enable callback' so that parent clock would
be already enabled.

One question is, mipi_tx_pll is used by dsi driver, but I does not see
dsi prepare_enable() mipi_tx_pll, how does this work?

Regards,
CK

> +
> +	mtk_mipi_tx_clear_bits(mipi_tx, MIPITX_PLL_CON4, RG_DSI_PLL_IBIAS);
> +
> +	mtk_mipi_tx_set_bits(mipi_tx, MIPITX_PLL_PWR, AD_DSI_PLL_SDM_PWR_ON);
> +	usleep_range(30, 100);
> +	mtk_mipi_tx_clear_bits(mipi_tx, MIPITX_PLL_PWR, AD_DSI_PLL_SDM_ISO_EN);
> +	pcw = div_u64(((u64)mipi_tx->data_rate * txdiv) << 24, 26000000);
> +	writel(pcw, mipi_tx->regs + MIPITX_PLL_CON0);
> +	mtk_mipi_tx_update_bits(mipi_tx, MIPITX_PLL_CON1, RG_DSI_PLL_POSDIV,
> +				txdiv0 << 8);
> +	usleep_range(1000, 2000);
> +	mtk_mipi_tx_set_bits(mipi_tx, MIPITX_PLL_CON1, RG_DSI_PLL_EN);
> +
> +	return 0;
> +}
> +
> +static void mtk_mipi_tx_pll_unprepare(struct clk_hw *hw)
> +{
> +	struct mtk_mipi_tx *mipi_tx = mtk_mipi_tx_from_clk_hw(hw);
> +
> +	dev_dbg(mipi_tx->dev, "unprepare\n");
> +
> +	mtk_mipi_tx_clear_bits(mipi_tx, MIPITX_PLL_CON1, RG_DSI_PLL_EN);
> +
> +	mtk_mipi_tx_set_bits(mipi_tx, MIPITX_PLL_PWR, AD_DSI_PLL_SDM_ISO_EN);
> +	mtk_mipi_tx_clear_bits(mipi_tx, MIPITX_PLL_PWR, AD_DSI_PLL_SDM_PWR_ON);
> +	clk_disable_unprepare(mipi_tx->ref_clk);
> +}
> +