Re: [PATCH] drm: edid: add support for E-DDC

On Tue, Aug 21, 2012 at 9:10 AM, Shirish S s.shirish@samsung.com 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@samsung.com

drivers/gpu/drm/drm_edid.c | 17 ++++++++++++----- 1 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index a8743c3..2c2996e 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;
  

Have you tested this on i915 with gmbus enabled? I'm asking since we don't implement the IGNORE_NAK flag and hence I'd expect spurious failures on displays that don't support E-DDC ...

Cheers, Daniel

    int ret, retries = 5;

    /* The core i2c driver will automatically retry the transfer if the

@@ -264,27 +266,32 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf, */ do { struct i2c_msg msgs[] = {

•                   {
  

•                   { /*set segment pointer */
  

•                           .addr   = DDC_SEGMENT_ADDR,
  

•                           .flags  = segFlags,
  

•                           .len    = 1,
  

•                           .buf    = &start,
  

•                   }, { /*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, 2);
  

•           ret = i2c_transfer(adapter, msgs, 3);
            if (ret == -ENXIO) {
                    DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
                                    adapter->name);
                    break;
            }
  

•   } while (ret != 2 && --retries);
  

•   } while (ret != 3 && --retries);
  
  

•   return ret == 2 ? 0 : -1;
  

•   return ret == 3 ? 0 : -1;
  

}

static bool drm_edid_is_zero(u8 *in_edid, int length)

1.7.0.4

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