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From:   Philip Chen <philipchen@chromium.org>
Date:   Wed, 15 Sep 2021 13:41:12 -0700
Message-ID: <CA+cxXhn-gLt37oyEq3wSh3qf=UkY=H6fY3ahC=gyhKhGwu_dXw@mail.gmail.com>
Subject: Re: [PATCH v3 3/3] drm/bridge: parade-ps8640: Add support for AUX channel
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Douglas Anderson <dianders@chromium.org>,
        Andrzej Hajda <a.hajda@samsung.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Robert Foss <robert.foss@linaro.org>,
        dri-devel <dri-devel@lists.freedesktop.org>
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Hi

On Tue, Sep 14, 2021 at 5:57 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> 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()?
Sure.
>
> > +               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));
>
Yes, thanks for the advice.
Will add this change to v4.

> > +       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?
Sure.
>
> > +                                       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?
Sure.
>
> > +               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?
I want to make it clear that we are returning the number of bytes that
we have read/written instead of some error code.
If you think it's not super helpful, I can just return data & SWAUX_M_MASK.

>
> > +       case SWAUX_STATUS_ACKM:
>
> Move this up and add fallthrough?
Thanks.
Will add this change to v4.
>
> > +               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
regmap_read() wants to read to an unsigned int, but buf is an u8 array.
To be safe, I read RDATA to data and then assign data to buf[i].

As regmap_read() should always read 1 byte at a time, should I just do:
regmap_read(map, PAGE0_SWAUX_RDATA, (unsigned int*)(buf + i))

>
>                 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;
> > +}