linux-kernel - Re: [PATCH v3 3/3] drm/bridge: parade-ps8640: Add support for AUX channel

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Date:   Tue, 14 Sep 2021 17:57:17 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Philip Chen <philipchen@...omium.org>
Cc:     dianders@...omium.org, Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 3/3] drm/bridge: parade-ps8640: Add support for AUX channel

Quoting Philip Chen (2021-09-14 16:28:45)
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> index 8d3e7a147170..dc349d729f5a 100644
> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> @@ -117,6 +144,129 @@ static inline struct ps8640 *bridge_to_ps8640(struct drm_bridge *e)
[...]
> +       case DP_AUX_I2C_WRITE:
> +       case DP_AUX_I2C_READ:
> +               break;
> +       default:
> +               return -EINVAL;
> +       }
> +
> +       ret = regmap_write(map, PAGE0_AUXCH_CFG3, AUXCH_CFG3_RESET);
> +       if (ret) {
> +               dev_err(dev, "failed to write PAGE0_AUXCH_CFG3: %d\n", ret);

Can we use DRM_DEV_ERROR()?

> +               return ret;
> +       }
> +
> +       /* Assume it's good */
> +       msg->reply = 0;
> +
> +       addr_len[0] = msg->address & 0xff;
> +       addr_len[1] = (msg->address >> 8) & 0xff;
> +       addr_len[2] = ((msg->request << 4) & SWAUX_CMD_MASK) |
> +               ((msg->address >> 16) & SWAUX_ADDR_19_16_MASK);

It really feels like this out to be possible with some sort of
cpu_to_le32() API. We're shoving msg->address into 3 bytes and then
adding in the request and some length. So we could do something like:

	u32 addr_len;

	addr_len = FIELD_PREP(SWAUX_ADDR_MASK, msg->address);
	addr_len |= FIELD_PREP(SWAUX_CMD_MASK, msg->request);
	if (len)
		addr_len |= FIELD_PREP(LEN_MASK, len - 1);
	else
		addr_len |= FIELD_PREP(LEN_MASK, SWAUX_NO_PAYLOAD );
	
	cpu_to_le32s(&addr_len);

	regmap_bulk_write(map, PAGE0_SWAUX_ADDR_7_0, &addr_len, sizeof(addr_len));

> +       addr_len[3] = (len == 0) ? SWAUX_NO_PAYLOAD :
> +                       ((len - 1) & SWAUX_LENGTH_MASK);
> +
> +       regmap_bulk_write(map, PAGE0_SWAUX_ADDR_7_0, addr_len,
> +                         ARRAY_SIZE(addr_len));
> +
> +       if (len && (request == DP_AUX_NATIVE_WRITE ||
> +                   request == DP_AUX_I2C_WRITE)) {
> +               /* Write to the internal FIFO buffer */
> +               for (i = 0; i < len; i++) {
> +                       ret = regmap_write(map, PAGE0_SWAUX_WDATA, buf[i]);
> +                       if (ret) {
> +                               dev_err(dev, "failed to write WDATA: %d\n",

DRM_DEV_ERROR?

> +                                       ret);
> +                               return ret;
> +                       }
> +               }
> +       }
> +
> +       regmap_write(map, PAGE0_SWAUX_CTRL, SWAUX_SEND);
> +
> +       /* Zero delay loop because i2c transactions are slow already */
> +       regmap_read_poll_timeout(map, PAGE0_SWAUX_CTRL, data,
> +                                !(data & SWAUX_SEND), 0, 50 * 1000);
> +
> +       regmap_read(map, PAGE0_SWAUX_STATUS, &data);
> +       if (ret) {
> +               dev_err(dev, "failed to read PAGE0_SWAUX_STATUS: %d\n", ret);

DRM_DEV_ERROR?

> +               return ret;
> +       }
> +
> +       switch (data & SWAUX_STATUS_MASK) {
> +       /* Ignore the DEFER cases as they are already handled in hardware */
> +       case SWAUX_STATUS_NACK:
> +       case SWAUX_STATUS_I2C_NACK:
> +               /*
> +                * The programming guide is not clear about whether a I2C NACK
> +                * would trigger SWAUX_STATUS_NACK or SWAUX_STATUS_I2C_NACK. So
> +                * we handle both cases together.
> +                */
> +               if (is_native_aux)
> +                       msg->reply |= DP_AUX_NATIVE_REPLY_NACK;
> +               else
> +                       msg->reply |= DP_AUX_I2C_REPLY_NACK;
> +
> +               len = data & SWAUX_M_MASK;
> +               return len;

Why no 'return data & SWAUX_M_MASK;' and skip the assignment?

> +       case SWAUX_STATUS_ACKM:

Move this up and add fallthrough?

> +               len = data & SWAUX_M_MASK;
> +               return len;
> +       case SWAUX_STATUS_INVALID:
> +               return -EOPNOTSUPP;
> +       case SWAUX_STATUS_TIMEOUT:
> +               return -ETIMEDOUT;
> +       }
> +
> +       if (len && (request == DP_AUX_NATIVE_READ ||
> +                   request == DP_AUX_I2C_READ)) {
> +               /* Read from the internal FIFO buffer */
> +               for (i = 0; i < len; i++) {
> +                       ret = regmap_read(map, PAGE0_SWAUX_RDATA, &data);
> +                       buf[i] = data;

Can drop a line

		ret = regmap_read(map, PAGE0_SWAUX_RDATA, buf + i);

> +                       if (ret) {
> +                               dev_err(dev, "failed to read RDATA: %d\n",
> +                                       ret);
> +                               return ret;
> +                       }
> +               }
> +       }
> +
> +       return len;
> +}