Re: [PATCH v7] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus
From: Jonathan Liu
Date: Wed Jun 28 2017 - 23:49:20 EST
Hi Chen-Yu,
On 29 June 2017 at 12:47, Chen-Yu Tsai <wens@xxxxxxxx> wrote:
> Hi,
>
> On Wed, Jun 28, 2017 at 6:52 PM, Jonathan Liu <net147@xxxxxxxxx> 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@xxxxxxxxx>
>> ---
>> 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
>
You're right it should be 100 kHz. I will fix that.
>> + */
>> + 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
>>
Any other comments?
Regards,
Jonathan