On Fri, Dec 05, 2014 at 02:28:18PM -0800, Sean Paul wrote: > On Fri, Dec 5, 2014 at 2:17 PM, Thierry Reding <thierry.reding@xxxxxxxxx> > wrote: > > > On Fri, Dec 05, 2014 at 01:48:42PM -0800, Sean Paul wrote: > > > On Tue, Dec 2, 2014 at 5:40 PM, David Ung <davidu@xxxxxxxxxx> wrote: > > > > > > > Fix DSI PHY HS Trail setting on Tegra. > > > > It is found that HS Trail is off -12% during compliance testing > > > > > > > > > > > [this time from the correct email address] > > > > > > Our timing tests pass now. > > > > > > Tested-by: Sean Paul <seanpaul@xxxxxxxxxxxx> > > > > Can describe what kinds of timing tests these are? I obviously lack the > > kind of equipment for this, but I'd still like to know how you get these > > results. > > > > > Hi Thierry, > The test that was failing was the THS-TRAIL test. You can find the details > at [1], test is 8.1.13. The time was 7.7ns too short (or 12%, as David > stated). > > I'm not sure how David arrived at the value he did to extend HS-TRAIL, but > that particular test is now passing. From reading the document that you linked to and comparing to the D-PHY specification (version 1.2, Table 14, Page 40), the proper formula for the HSTrail parameter would be: max(n * 8 * period, 60 + n * 4 * period) I suspect that the additional 3 * period * 8 in this patch is derived from the note about "n", which is 1 for forward-direction high-speed mode and 4 for reverse-direction high-speed mode. Translating this to the code, the correct line would really be: timing->hstrail = max(4 * 8 * period, 60 + 4 * 4 * period); Since the "n" parameter appears in the second term, too. Also this is not Tegra-specific after all, so mipi_dphy_timing_get_default() indeed is the right place for it. How about the attached patch? Thierry
From 3399b7247fdc9609daea9919c444326fb9ddbdac Mon Sep 17 00:00:00 2001 From: David Ung <davidu@xxxxxxxxxx> Date: Fri, 5 Dec 2014 15:30:05 -0800 Subject: [PATCH] drm/tegra: dsi: Adjust D-PHY timing Compliance testing shows that HS Trail is off by -12%. Increase the HS Trail time to make this test pass. Signed-off-by: David Ung <davidu@xxxxxxxxxx> [treding@xxxxxxxxxx: update specification references, add comment] Signed-off-by: Thierry Reding <treding@xxxxxxxxxx> --- drivers/gpu/drm/tegra/mipi-phy.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/tegra/mipi-phy.c b/drivers/gpu/drm/tegra/mipi-phy.c index 486d19d589c8..ba2ae6511957 100644 --- a/drivers/gpu/drm/tegra/mipi-phy.c +++ b/drivers/gpu/drm/tegra/mipi-phy.c @@ -12,9 +12,9 @@ #include "mipi-phy.h" /* - * Default D-PHY timings based on MIPI D-PHY specification. Derived from - * the valid ranges specified in Section 5.9 of the D-PHY specification - * with minor adjustments. + * Default D-PHY timings based on MIPI D-PHY specification. Derived from the + * valid ranges specified in Section 6.9, Table 14, Page 40 of the D-PHY + * specification (v1.2) with minor adjustments. */ int mipi_dphy_timing_get_default(struct mipi_dphy_timing *timing, unsigned long period) @@ -34,7 +34,20 @@ int mipi_dphy_timing_get_default(struct mipi_dphy_timing *timing, timing->hszero = 145 + 5 * period; timing->hssettle = 85 + 6 * period; timing->hsskip = 40; - timing->hstrail = max(8 * period, 60 + 4 * period); + + /* + * The MIPI D-PHY specification (Section 6.9, v1.2, Table 14, Page 40) + * contains this formula as: + * + * T_HS-TRAIL = max(n * 8 * period, 60 + n * 4 * period) + * + * where n = 1 for forward-direction HS mode and n = 4 for reverse- + * direction HS mode. There's only one setting and this function does + * not parameterize on anything other that period, so this code will + * assumes that reverse-direction HS mode is supported and uses n = 4. + */ + timing->hstrail = max(4 * 8 * period, 60 + 4 * 4 * period); + timing->init = 100000; timing->lpx = 60; timing->taget = 5 * timing->lpx; @@ -46,8 +59,8 @@ int mipi_dphy_timing_get_default(struct mipi_dphy_timing *timing, } /* - * Validate D-PHY timing according to MIPI Alliance Specification for D-PHY, - * Section 5.9 "Global Operation Timing Parameters". + * Validate D-PHY timing according to MIPI D-PHY specification (v1.2, Section + * Section 6.9 "Global Operation Timing Parameters"). */ int mipi_dphy_timing_validate(struct mipi_dphy_timing *timing, unsigned long period) -- 2.1.3
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