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

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Date:   Sat, 18 May 2019 15:51:32 +0800
From:   Jitao Shi <jitao.shi@...iatek.com>
To:     CK Hu <ck.hu@...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

On Mon, 2019-05-06 at 17:17 +0800, CK Hu wrote:
> 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
> 

The mipi_tx can be accessed after clk_prepare_enable(mipi_tx->ref_clk);

So place the clk_prepare_enable(mipi_tx->ref_clk) before accessing
mipitx.

mipi_tx_pll is enable by mtk_mipi_tx_power_on() in mtk_mip_tx.c.
clk_prepare_enable(mipi_tx->pll) will enable mipi_tx_pll.

Beset Regards
Jitao

> > +
> > +	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);
> > +}
> > +
> 
>