[PATCH V3] drm: edid: add support for E-DDC
Shirish S
shirish.s12 at gmail.com
Fri Aug 24 17:26:56 PDT 2012
Thanks for the comments, will upload patch set
with your comments.
On Fri, Aug 24, 2012 at 11:20 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> 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 at samsung.com>
> > ---
> > 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
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48
> _______________________________________________
> dri-devel mailing list
> dri-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
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