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Date: Thu, 29 Jun 2017 10:47:53 +0800
From: Chen-Yu Tsai <wens@...e.org>
To: Jonathan Liu <net147@...il.com>
Cc: Maxime Ripard <maxime.ripard@...e-electrons.com>,
David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
dri-devel <dri-devel@...ts.freedesktop.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v7] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus
Hi,
On Wed, Jun 28, 2017 at 6:52 PM, Jonathan Liu <net147@...il.com> wrote:
> The documentation for drm_do_get_edid in drivers/gpu/drm/drm_edid.c states:
> "As in the general case the DDC bus is accessible by the kernel at the I2C
> level, drivers must make all reasonable efforts to expose it as an I2C
> adapter and use drm_get_edid() instead of abusing this function."
>
> Exposing the DDC bus as an I2C adapter is more beneficial as it can be used
> for purposes other than reading the EDID such as modifying the EDID or
> using the HDMI DDC pins as an I2C bus through the I2C dev interface from
> userspace (e.g. i2c-tools).
>
> Implement this for A10s.
>
> Signed-off-by: Jonathan Liu <net147@...il.com>
> ---
> Changes for v7:
> - Fix mixed declarations and code compiler warning for level variable
>
> Changes for v6:
> - Use fixed byte time of 100 us instead of dynamically calculating from DDC
> clock that is set to a fixed 100 MHz rate anyway
> - Change is_fifo_flag_unset to not read the status register as well to be
> more consistent with is_err_status
>
> Changes for v5:
> - Use devm_kzalloc instead of devm_kmemdup and remove const struct i2c_adapter
> - Rework to use readl_poll_timeout for checking FIFO status
>
> Changes for v4:
> - Carry over copyright from initial I2C code into sun4i_hdmi_i2c.c
> - Clean up indentation in sun4i_hdmi.h
> - Rename SUN4I_HDMI_DDC_MAX_TRANSFER_SIZE to SUN4I_HDMI_DDC_BYTE_COUNT_MAX
> and group it under the SUN4I_HDMI_DDC_BYTE_COUNT_REG define, changing the
> value to use the GENMASK macro to make it clear that it is derived from
> the width of the field in the register
> - Fix SUN4I_HDMI_DDC_INT_STATUS_DDC_TX_FIFO_UNDERFLOW typo which should be
> SUN4I_HDMI_DDC_INT_STATUS_DDC_TX_FIFO_OVERFLOW
> - Remove redundant rewriting of SUN4I_HDMI_DDC_INT_STATUS_REG register
> - Change struct i2c_adapter to be const by using devm_kmemdup on creation
> - Return -ETIMEDOUT instead of -EIO if there is timeout while transferring an
> I2C message
> - Instead of waiting for 1-2 bytes to transfer, wait for the time it would
> take for remaining bytes to transfer (limited by FIFO size)
> - Add additional comments
>
> Changes for v3:
> - Explain why drm_do_get_edid should be used and why it's better to expose it
> as an I2C adapter in commit message
> - Reorder bit defines in descending order for consistency
> - Keep old unused macros instead of removing them
> - The v2 algorithm split large transfers into 16 byte transfers but this may
> cause a large single write to be treated as multiple writes causing data
> corruption. The algorithm has been reworked to not split larger transfers
> and make more use of the FIFO to avoid this.
> - Moved the creation of the DDC clock from sun4i_hdmi_enc.c to
> sun4i_hdmi_i2c.c
> - Reformatted code
> - Instead of masking bits that we don't want to check for errors, explicitly
> check the error bits
> - Clear error bits at start of transfer in case of error from previous transfer
> - Poll for completion of FIFO clear after setting FIFO clear bit
>
> Changes for v2:
> - Rebased against Maxime's sunxi-drm/for-next branch
> - Fix up error paths in sun4i_hdmi_bind so that the I2C adapter is deleted if
> any of the calls after the I2C adapter is created fails
> - Remove unnecessary includes in sun4i_hdmi_i2c.c
>
> drivers/gpu/drm/sun4i/Makefile | 1 +
> drivers/gpu/drm/sun4i/sun4i_hdmi.h | 23 ++++
> drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 101 ++------------
> drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c | 234 +++++++++++++++++++++++++++++++++
> 4 files changed, 269 insertions(+), 90 deletions(-)
> create mode 100644 drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c
>
[...]
> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c
> new file mode 100644
> index 000000000000..ce954ee25ae4
> --- /dev/null
> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c
> @@ -0,0 +1,234 @@
[...]
> +static int fifo_transfer(struct sun4i_hdmi *hdmi, u8 *buf, int len, bool read)
> +{
> + /*
> + * 1 byte takes 9 clock cycles (8 bits + 1 ACK) = 90 us for 100 MHz
> + * clock. As clock rate is fixed, just round it up to 100 us.
This looks fishy. I2C busses are never that fast. Maybe kHz?
ChenYu
> + */
> + const unsigned long byte_time_ns = 100;
> + u32 int_status;
> + u32 fifo_status;
> + /* Read needs empty flag unset, write needs full flag unset */
> + u32 flag = read ? SUN4I_HDMI_DDC_FIFO_STATUS_EMPTY :
> + SUN4I_HDMI_DDC_FIFO_STATUS_FULL;
> + int level;
> + int ret;
> +
> + /* Wait until error or FIFO ready */
> + ret = readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG,
> + int_status,
> + is_err_status(int_status) ||
> + is_fifo_flag_unset(fifo_status =
> + read_fifo_status(hdmi),
> + flag),
> + min(len, SUN4I_HDMI_DDC_FIFO_SIZE) *
> + byte_time_ns, 100000);
> +
> + if (is_err_status(int_status))
> + return -EIO;
> + if (ret)
> + return -ETIMEDOUT;
> +
> + /* Read FIFO level */
> + level = (int)(fifo_status & SUN4I_HDMI_DDC_FIFO_STATUS_LEVEL_MASK);
> +
> + /* Limit transfer length using FIFO level to avoid underflow/overflow */
> + len = min(len, read ? level : (SUN4I_HDMI_DDC_FIFO_SIZE - level));
> +
> + if (read)
> + readsb(hdmi->base + SUN4I_HDMI_DDC_FIFO_DATA_REG, buf, len);
> + else
> + writesb(hdmi->base + SUN4I_HDMI_DDC_FIFO_DATA_REG, buf, len);
> +
> + return len;
> +}
> +
> +static int xfer_msg(struct sun4i_hdmi *hdmi, struct i2c_msg *msg)
> +{
> + int i, len;
> + u32 reg;
> +
> + /* Clear errors */
> + reg = readl(hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG);
> + reg &= ~SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK;
> + writel(reg, hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG);
> +
> + /* Set FIFO direction */
> + reg = readl(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
> + reg &= ~SUN4I_HDMI_DDC_CTRL_FIFO_DIR_MASK;
> + reg |= (msg->flags & I2C_M_RD) ?
> + SUN4I_HDMI_DDC_CTRL_FIFO_DIR_READ :
> + SUN4I_HDMI_DDC_CTRL_FIFO_DIR_WRITE;
> + writel(reg, hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
> +
> + /* Set I2C address */
> + writel(SUN4I_HDMI_DDC_ADDR_SLAVE(msg->addr),
> + hdmi->base + SUN4I_HDMI_DDC_ADDR_REG);
> +
> + /* Clear FIFO */
> + reg = readl(hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG);
> + writel(reg | SUN4I_HDMI_DDC_FIFO_CTRL_CLEAR,
> + hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG);
> + if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG,
> + reg,
> + !(reg & SUN4I_HDMI_DDC_FIFO_CTRL_CLEAR),
> + 100, 100000))
> + return -EIO;
> +
> + /* Set transfer length */
> + writel(msg->len, hdmi->base + SUN4I_HDMI_DDC_BYTE_COUNT_REG);
> +
> + /* Set command */
> + writel(msg->flags & I2C_M_RD ?
> + SUN4I_HDMI_DDC_CMD_IMPLICIT_READ :
> + SUN4I_HDMI_DDC_CMD_IMPLICIT_WRITE,
> + hdmi->base + SUN4I_HDMI_DDC_CMD_REG);
> +
> + /* Start command */
> + reg = readl(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
> + writel(reg | SUN4I_HDMI_DDC_CTRL_START_CMD,
> + hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
> +
> + /* Transfer bytes */
> + for (i = 0; i < msg->len; i += len) {
> + len = fifo_transfer(hdmi, msg->buf + i, msg->len - i,
> + msg->flags & I2C_M_RD);
> + if (len <= 0)
> + return len;
> + }
> +
> + /* Wait for command to finish */
> + if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG,
> + reg,
> + !(reg & SUN4I_HDMI_DDC_CTRL_START_CMD),
> + 100, 100000))
> + return -EIO;
> +
> + /* Check for errors */
> + reg = readl(hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG);
> + if ((reg & SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK) ||
> + !(reg & SUN4I_HDMI_DDC_INT_STATUS_TRANSFER_COMPLETE)) {
> + return -EIO;
> + }
> +
> + return 0;
> +}
> +
> +static int sun4i_hdmi_i2c_xfer(struct i2c_adapter *adap,
> + struct i2c_msg *msgs, int num)
> +{
> + struct sun4i_hdmi *hdmi = i2c_get_adapdata(adap);
> + u32 reg;
> + int err, i, ret = num;
> +
> + for (i = 0; i < num; i++) {
> + if (!msgs[i].len)
> + return -EINVAL;
> + if (msgs[i].len > SUN4I_HDMI_DDC_BYTE_COUNT_MAX)
> + return -EINVAL;
> + }
> +
> + /* Reset I2C controller */
> + writel(SUN4I_HDMI_DDC_CTRL_ENABLE | SUN4I_HDMI_DDC_CTRL_RESET,
> + hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
> + if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG, reg,
> + !(reg & SUN4I_HDMI_DDC_CTRL_RESET),
> + 100, 2000))
> + return -EIO;
> +
> + writel(SUN4I_HDMI_DDC_LINE_CTRL_SDA_ENABLE |
> + SUN4I_HDMI_DDC_LINE_CTRL_SCL_ENABLE,
> + hdmi->base + SUN4I_HDMI_DDC_LINE_CTRL_REG);
> +
> + clk_prepare_enable(hdmi->ddc_clk);
> + clk_set_rate(hdmi->ddc_clk, 100000);
Indeed the clock rate is 100 kHz.
ChenYu
> +
> + for (i = 0; i < num; i++) {
> + err = xfer_msg(hdmi, &msgs[i]);
> + if (err) {
> + ret = err;
> + break;
> + }
> + }
> +
> + clk_disable_unprepare(hdmi->ddc_clk);
> + return ret;
> +}
> +
> +static u32 sun4i_hdmi_i2c_func(struct i2c_adapter *adap)
> +{
> + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
> +}
> +
> +static const struct i2c_algorithm sun4i_hdmi_i2c_algorithm = {
> + .master_xfer = sun4i_hdmi_i2c_xfer,
> + .functionality = sun4i_hdmi_i2c_func,
> +};
> +
> +int sun4i_hdmi_i2c_create(struct device *dev, struct sun4i_hdmi *hdmi)
> +{
> + struct i2c_adapter *adap;
> + int ret = 0;
> +
> + ret = sun4i_ddc_create(hdmi, hdmi->tmds_clk);
> + if (ret)
> + return ret;
> +
> + adap = devm_kzalloc(dev, sizeof(*adap), GFP_KERNEL);
> + if (!adap)
> + return -ENOMEM;
> +
> + adap->owner = THIS_MODULE;
> + adap->class = I2C_CLASS_DDC;
> + adap->algo = &sun4i_hdmi_i2c_algorithm;
> + strlcpy(adap->name, "sun4i_hdmi_i2c adapter", sizeof(adap->name));
> + i2c_set_adapdata(adap, hdmi);
> +
> + ret = i2c_add_adapter(adap);
> + if (ret)
> + return ret;
> +
> + hdmi->i2c = adap;
> +
> + return ret;
> +}
> --
> 2.13.1
>
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