linux-kernel - Re: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort driver

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Date:   Wed, 8 Jun 2022 16:54:27 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     CK Hu <ck.hu@...iatek.com>,
        Guillaume Ranquet <granquet@...libre.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chunfeng Yun (云春峰) 
        <Chunfeng.Yun@...iatek.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, Helge Deller <deller@....de>,
        Jitao Shi (石记涛) 
        <jitao.shi@...iatek.com>
CC:     Markus Schneider-Pargmann <msp@...libre.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH v10 18/21] drm/mediatek: Add mt8195 Embedded DisplayPort
 driver

On Wed, 2022-06-08 at 16:45 +0800, CK Hu wrote:
> Hi, Rex:
> 
> On Mon, 2022-05-23 at 12:47 +0200, Guillaume Ranquet wrote:
> > From: Markus Schneider-Pargmann <msp@...libre.com>
> > 
> > This patch adds a DisplayPort driver for the Mediatek mt8195 SoC.
> > 
> > It supports the mt8195, the embedded DisplayPort units. It offers
> > DisplayPort 1.4 with up to 4 lanes.
> > 
> > The driver creates a child device for the phy. The child device
> > will
> > never exist without the parent being active. As they are sharing a
> > register range, the parent passes a regmap pointer to the child so
> > that
> > both can work with the same register range. The phy driver sets
> > device
> > data that is read by the parent to get the phy device that can be
> > used
> > to control the phy properties.
> > 
> > This driver is based on an initial version by
> > Jason-JH.Lin <jason-jh.lin@...iatek.com>.
> > 
> > Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> > Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> > ---
> 
> [snip]
> 
> > +
> > +static bool mtk_dp_set_swing_pre_emphasis(struct mtk_dp *mtk_dp,
> > int
> > lane_num,
> > +					  int swing_val, int
> > preemphasis)
> 
> The return value is never processed, so let this function to be void.
> 
> Regards,
> CK
> 

Hello CK,

ok, I will drop this.
Actually, I change "mtk_dp_write", "mtk_dp_update_bits" and
"mtk_dp_bulk_16bit_write" to return void. I don't think we need to
handle the issue that we failed to set registers. If we failed to set
register, it's because hw is not enable.

Therefore, I drop this and we can reduce many lines of codes.

BRs,
Bo-Chen
> > +{
> > +	int ret;
> > +
> > +	u32 lane_shift = lane_num * DP_TX1_VOLT_SWING_SHIFT;
> > +
> > +	if (lane_num < 0 || lane_num > 3)
> 
> lane_num < 0 would not happen. lane_num > 3 only if device tree max
> lane is wrong. So I would like to checkout max lane when parsing
> device
> tree instead of checking here.
> > +		return false;
> > +
> > +	dev_dbg(mtk_dp->dev,
> > +		"link training swing_val= 0x%x, preemphasis = 0x%x\n",
> > +		swing_val, preemphasis);
> > +
> > +	ret = mtk_dp_update_bits(mtk_dp, MTK_DP_TOP_SWING_EMP,
> > +				 swing_val << (DP_TX0_VOLT_SWING_SHIFT
> > + lane_shift),
> > +				 DP_TX0_VOLT_SWING_MASK << lane_shift);
> > +	if (ret)
> > +		return ret;
> > +	ret = mtk_dp_update_bits(mtk_dp, MTK_DP_TOP_SWING_EMP,
> > +				 preemphasis << (DP_TX0_PRE_EMPH_SHIFT
> > + lane_shift),
> > +				 DP_TX0_PRE_EMPH_MASK << lane_shift);
> > +
> > +	return !ret;
> > +}
> > +
> 
>