linux-kernel - Re: [PATCH v14 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

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Date:   Thu, 14 Jul 2022 16:52:29 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     CK Hu <ck.hu@...iatek.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "mripard@...nel.org" <mripard@...nel.org>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "deller@....de" <deller@....de>,
        "airlied@...ux.ie" <airlied@...ux.ie>
CC:     "msp@...libre.com" <msp@...libre.com>,
        "granquet@...libre.com" <granquet@...libre.com>,
        Jitao Shi (石记涛) 
        <jitao.shi@...iatek.com>,
        "wenst@...omium.org" <wenst@...omium.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        LiangXu Xu (徐亮) 
        <LiangXu.Xu@...iatek.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-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v14 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort
 driver

On Wed, 2022-07-13 at 17:31 +0800, CK Hu wrote:
> Hi, Bo-Chen:
> 
> On Tue, 2022-07-12 at 19:12 +0800, Bo-Chen Chen wrote:
> > From: Markus Schneider-Pargmann <msp@...libre.com>
> > 
> > This patch adds a embedded 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
> > Jitao shi <jitao.shi@...iatek.com>
> > 
> > Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> > Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> > Signed-off-by: Bo-Chen Chen <rex-bc.chen@...iatek.com>
> > ---
> 
> [snip]
> 
> > +
> > +static void mtk_dp_bulk_16bit_write(struct mtk_dp *mtk_dp, u32
> > offset, u8 *buf,
> > +				    size_t length)
> 
> The offset would always be MTK_DP_AUX_P0_3708, so drop offset and use
> MTK_DP_AUX_P0_3708 directly.
> 

Hello CK,

I don't think it's a good idea. this function is a fucntion of writing
registers. I want to keep the offset variable.

> > +{
> > +	int i;
> > +	int num_regs = (length + 1) / 2;
> > +
> > +	/* 2 bytes per register */
> > +	for (i = 0; i < num_regs; i++) {
> > +		u32 val = buf[i * 2] |
> > +			  (i * 2 + 1 < length ? buf[i * 2 + 1] << 8 :
> > 0);
> > +
> > +		if (mtk_dp_write(mtk_dp, offset + i * 4, val))
> > +			return;
> > +	}
> 
> for (i = 0; i < length; i += 2) {
> 	val = buf[i] | (i + 1 < length ? buf[i + 1] << 8 : 0);
> 	if (mtk_dp_write(mtk_dp, MTK_DP_AUX_P0_3708 + i * 2, val))
> 		return;
> }
> 

ok.

BRs,
Bo-Chen

> Regards,
> CK
> 
> > +}
> > +
> 
>