Re: [v2 3/3] drm/mediatek: add mipi_tx driver for mt8183

[CK Hu]

On Sat, 2019-05-18 at 15:51 +0800, Jitao Shi wrote:
> 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@xxxxxxxxxxxx>
> > > ---
> > >  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.

OK, so it start from dsi driver. The callstack is:

phy_power_on(dsi->phy);
-> mtk_mipi_tx_power_on()
--> clk_prepare_enable(mipi_tx->pll);
---> mtk_mipi_tx_pll_prepare();

In clk_prepare_enable(), it separately call clk_prepare() and
clk_enable(). When clk_prepare(), it prepare the parent clock then
prepare this clock. When clk_enable(), it enable the parent clock then
enable this clock. So this would result in the sequence:

1. Prepare mipi_tx->ref_clk
2. Prepare mipi_tx->pll
3. Enable mipi_tx->ref_clk
4. Enable mipi_tx->pll

You say 'So place the clk_prepare_enable(mipi_tx->ref_clk) before
accessing mipitx.', so the step 1 and step 3 is equal to
clk_prepare_enable(mipi_tx->ref_clk), so I require you to access mipitx
in step 4, not in step 2.

Regards,
CK

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