lkml.org 
[lkml]   [2019]   [Apr]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.4 068/168] drm/dp/mst: Configure no_stop_bit correctly for remote i2c xfers
    Date
    [ Upstream commit c978ae9bde582e82a04c63a4071701691dd8b35c ]

    We aren't supposed to force a stop+start between every i2c msg
    when performing multi message transfers. This should eg. cause
    the DDC segment address to be reset back to 0 between writing
    the segment address and reading the actual EDID extension block.

    To quote the E-DDC spec:
    "... this standard requires that the segment pointer be
    reset to 00h when a NO ACK or a STOP condition is received."

    Since we're going to touch this might as well consult the
    I2C_M_STOP flag to determine whether we want to force the stop
    or not.

    Cc: Brian Vincent <brainn@gmail.com>
    Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20180928180403.22499-1-ville.syrjala@linux.intel.com
    Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/drm_dp_mst_topology.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
    index 5a1bafb5ecbb..ff12d926eb65 100644
    --- a/drivers/gpu/drm/drm_dp_mst_topology.c
    +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
    @@ -3019,6 +3019,7 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
    msg.u.i2c_read.transactions[i].i2c_dev_id = msgs[i].addr;
    msg.u.i2c_read.transactions[i].num_bytes = msgs[i].len;
    msg.u.i2c_read.transactions[i].bytes = msgs[i].buf;
    + msg.u.i2c_read.transactions[i].no_stop_bit = !(msgs[i].flags & I2C_M_STOP);
    }
    msg.u.i2c_read.read_i2c_device_id = msgs[num - 1].addr;
    msg.u.i2c_read.num_bytes_read = msgs[num - 1].len;
    --
    2.19.1


    \
     
     \ /
      Last update: 2019-04-24 20:06    [W:4.786 / U:0.832 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site