linux-kernel - Re: [PATCH 1/4] drm/bridge: ti-sn65dsi86: Combine register accesses in ti_sn_aux

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Date:   Thu, 29 Oct 2020 18:18:00 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Douglas Anderson <dianders@...omium.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sean Paul <seanpaul@...omium.org>
Subject: Re: [PATCH 1/4] drm/bridge: ti-sn65dsi86: Combine register accesses in ti_sn_aux_transfer()

Quoting Stephen Boyd (2020-10-28 18:11:51)
> @@ -72,6 +74,7 @@
>  #define SN_AUX_ADDR_19_16_REG                  0x74
>  #define SN_AUX_ADDR_15_8_REG                   0x75
>  #define SN_AUX_ADDR_7_0_REG                    0x76
> +#define SN_AUX_ADDR_MASK                       GENMASK(19, 0)
>  #define SN_AUX_LENGTH_REG                      0x77
>  #define SN_AUX_CMD_REG                         0x78
>  #define  AUX_CMD_SEND                          BIT(0)
> @@ -841,11 +844,13 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
>         struct ti_sn_bridge *pdata = aux_to_ti_sn_bridge(aux);
>         u32 request = msg->request & ~DP_AUX_I2C_MOT;
>         u32 request_val = AUX_CMD_REQ(msg->request);
> -       u8 *buf = (u8 *)msg->buffer;
> +       u8 *buf = msg->buffer;
> +       unsigned int len = msg->size;
>         unsigned int val;
> -       int ret, i;
> +       int ret;
> +       u8 addr_len[SN_AUX_LENGTH_REG + 1 - SN_AUX_ADDR_19_16_REG];

I realize now that the SN_AUX_CMD_REG is also here and it has a "go bit"
in it. We can combine another register write here by writing out the
address, length, and request in one go. I rolled that into v2.