On Fri, Aug 24, 2012 at 02:56:50PM +0530, Shirish S wrote:
> The current logic for probing ddc is limited to
> 2 blocks (256 bytes), this patch adds support
> for the 4 block (512) data.
>
> To do this, a single 8-bit segment index is
> passed to the display via the I2C address 30h.
> Data from the selected segment is then immediately
> read via the regular DDC2 address using a repeated
> I2C 'START' signal.
>
> Signed-off-by: Shirish S <s.shirish@xxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_edid.c | 83 ++++++++++++++++++++++++++++++++-----------
> 1 files changed, 62 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a8743c3..a10a130 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -254,6 +254,8 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
> int block, int len)
> {
> unsigned char start = block * EDID_LENGTH;
> + unsigned char segment = block >> 1;
> + unsigned short segFlags = segment ? 0 : I2C_M_IGNORE_NAK;
You can inline segFlags to the only place it's used.
> int ret, retries = 5;
>
> /* The core i2c driver will automatically retry the transfer if the
> @@ -262,29 +264,68 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
> * generate spurious NAKs and timeouts. Retrying the transfer
> * of the individual block a few times seems to overcome this.
> */
> - do {
> - struct i2c_msg msgs[] = {
> - {
> - .addr = DDC_ADDR,
> - .flags = 0,
> - .len = 1,
> - .buf = &start,
> - }, {
> - .addr = DDC_ADDR,
> - .flags = I2C_M_RD,
> - .len = len,
> - .buf = buf,
> + switch (segment) {
> + /* To reduce traffic on I2C, we request the i2c xfer
> + * for segment addr only if 4 block edid data is
> + * present.
> + * 0 : DDC
> + * 1 : E-DDC
> + */
This comment is a bit misleading: We don't avoid the segment xfer to
reduce i2c traffic, but to avoid upsetting any non-compliant screens.
> + case 0:
> + do {
Keeping the loop as the outermost would imo be clearer and avoid
duplicating it (it also would make the patch a bit smaller). You could
even do a trick with the msgs array like this:
msgs[] = { full i2c xfer including segment addr}
xfers = 3;
/* Avoid sending the segment addr to not upset non-compliant ddc
* monitors. */
if (!segments)
msgs++, len--;
i2c_transefer(adapter, msgs, len);
Also, I think it'd be good to set the IGNORE_NAK on the start addre
transfer, too (but in a separate patch). At least I think we've seen
screens out there that need this :(
Yours, Daniel
> + struct i2c_msg msgs[] = {
> + {
> + .addr = DDC_ADDR,
> + .flags = 0,
> + .len = 1,
> + .buf = &start,
> + }, {
> + .addr = DDC_ADDR,
> + .flags = I2C_M_RD,
> + .len = len,
> + .buf = buf,
> + }
> + };
> + ret = i2c_transfer(adapter, msgs, 2);
> + if (ret == -ENXIO) {
> + DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
> + adapter->name);
> + break;
> }
> - };
> - ret = i2c_transfer(adapter, msgs, 2);
> - if (ret == -ENXIO) {
> - DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
> - adapter->name);
> - break;
> - }
> - } while (ret != 2 && --retries);
> + } while (ret != 2 && --retries);
> +
> + return ret == 2 ? 0 : -1;
> + case 1:
> + do {
> + struct i2c_msg msgs[] = {
> + { /*set segment pointer */
> + .addr = DDC_SEGMENT_ADDR,
> + .flags = segFlags,
> + .len = 1,
> + .buf = &segment,
> + }, { /*set offset */
> + .addr = DDC_ADDR,
> + .flags = 0,
> + .len = 1,
> + .buf = &start,
> + }, { /*set data */
> + .addr = DDC_ADDR,
> + .flags = I2C_M_RD,
> + .len = len,
> + .buf = buf,
> + }
> + };
> + ret = i2c_transfer(adapter, msgs, 3);
> + if (ret == -ENXIO) {
> + DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
> + adapter->name);
> + break;
> + }
> + } while (ret != 3 && --retries);
>
> - return ret == 2 ? 0 : -1;
> + return ret == 3 ? 0 : -1;
> + }
> + return -1;
> }
>
> static bool drm_edid_is_zero(u8 *in_edid, int length)
> --
> 1.7.0.4
>
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--
Daniel Vetter
Mail: daniel@xxxxxxxx
Mobile: +41 (0)79 365 57 48
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