Re: [PATCH] OMAPDSS: HDMI: Cache EDID

On 25 June 2012 12:05, Tomi Valkeinen [off-list ref] wrote:

On Sat, 2012-06-23 at 13:36 +0530, jaswinder.singh@linaro.org wrote:

quoted

From: Jassi Brar <redacted>

We can easily keep track of latest EDID from the display and hence avoid
expensive EDID re-reads over I2C.
This could also help some cheapo displays that provide EDID reliably only
immediately after asserting HPD and not later.
Even with good displays, there is something in OMAPDSS that apparantly
messes up DDC occasionally while EDID is being read, giving the
  "operation stopped when reading edid" error.

Signed-off-by: Jassi Brar <redacted>
---
 drivers/video/omap2/dss/hdmi.c            |    1 +
 drivers/video/omap2/dss/ti_hdmi.h         |    2 ++
 drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c |   23 ++++++++++++++++++++---
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/video/omap2/dss/hdmi.c b/drivers/video/omap2/dss/hdmi.c
index 900e621..0a8c825 100644
--- a/drivers/video/omap2/dss/hdmi.c
+++ b/drivers/video/omap2/dss/hdmi.c

@@ -764,6 +764,7 @@ static int __init omapdss_hdmihw_probe(struct platform_device *pdev)

      hdmi.ip_data.core_av_offset = HDMI_CORE_AV;
      hdmi.ip_data.pll_offset = HDMI_PLLCTRL;
      hdmi.ip_data.phy_offset = HDMI_PHY;
+     hdmi.ip_data.edid_len = 0; /* Invalidate EDID Cache */
      mutex_init(&hdmi.ip_data.lock);

Your HDMI patches seem to depend on each other. Please post them as a
proper patch series, instead of each one separately.

They don't depend functionality wise. Any fix can be accepted
regardless of others.
I deliberately avoided a series, because revision of just one could
require resending 3, otherwise
perfectly OK, patches. I just wanted to limit the noise.
I understand, 'git am' might complain but I think that should be trivial to fix.
I am perfectly OK to resend as a patch series, if you want.

quoted

      hdmi_panel_init();

diff --git a/drivers/video/omap2/dss/ti_hdmi.h b/drivers/video/omap2/dss/ti_hdmi.h
index cc292b8..4735860 100644
--- a/drivers/video/omap2/dss/ti_hdmi.h
+++ b/drivers/video/omap2/dss/ti_hdmi.h

@@ -178,6 +178,8 @@ struct hdmi_ip_data {

      /* ti_hdmi_4xxx_ip private data. These should be in a separate struct */
      int hpd_gpio;
      struct mutex lock;
+     u8 edid_cached[256];
+     unsigned edid_len;
 };
 int ti_hdmi_4xxx_phy_enable(struct hdmi_ip_data *ip_data);
 void ti_hdmi_4xxx_phy_disable(struct hdmi_ip_data *ip_data);

diff --git a/drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c b/drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c
index 04acca9..2633ade 100644
--- a/drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c
+++ b/drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c

@@ -243,10 +243,13 @@ static int hdmi_check_hpd_state(struct hdmi_ip_data *ip_data)

      hpd = gpio_get_value(ip_data->hpd_gpio);

-     if (hpd)
+     if (hpd) {
              r = hdmi_set_phy_pwr(ip_data, HDMI_PHYPWRCMD_TXON);
-     else
+     } else {
+             /* Invalidate EDID Cache */
+             ip_data->edid_len = 0;
              r = hdmi_set_phy_pwr(ip_data, HDMI_PHYPWRCMD_LDOON);
+     }

      if (r) {
              DSSERR("Failed to %s PHY TX power\n",

@@ -454,6 +457,11 @@ int ti_hdmi_4xxx_read_edid(struct hdmi_ip_data *ip_data,

 {
      int r, l;

+     if (ip_data->edid_len) {
+             memcpy(edid, ip_data->edid_cached, ip_data->edid_len);
+             return ip_data->edid_len;
+     }
+
      if (len < 128)
              return -EINVAL;

@@ -474,12 +482,21 @@ int ti_hdmi_4xxx_read_edid(struct hdmi_ip_data *ip_data,

              l += 128;
      }

+     ip_data->edid_len = l;
+     memcpy(ip_data->edid_cached, edid, l);
+
      return l;
 }

 bool ti_hdmi_4xxx_detect(struct hdmi_ip_data *ip_data)
 {
-     return gpio_get_value(ip_data->hpd_gpio);
+     if (gpio_get_value(ip_data->hpd_gpio))
+             return true;
+
+     /* Invalidate EDID Cache */
+     ip_data->edid_len = 0;
+
+     return false;

Why is this needed? The HPD interrupt should handle this already. And if
the HPD interrupt doesn't work for some reason, this won't work either,
as the user can plug and unplug his HDMI monitors a thousand times
between two detect calls.

I thought it is almost impossible to unplug->plug cycle the HDMI cable
even twice a second, let alone 1000 times against the 10Hz .detect()
poll  :)    Or you mean some relay controlled HDMI switching
mechanism?

 Anyways, that is not the point of this patch. This patch only aims to
avoid un-ncessary EDID reads while doing its best to make sure we
invalidate EDID 'as soon as possible'.

Thanks.