On 03/23/2017 10:23 AM, Jani Nikula wrote:
On Thu, 23 Mar 2017, Clint Taylor <clinton.a.taylor@xxxxxxxxx> wrote:
On 03/23/2017 05:30 AM, Jani Nikula wrote:
On Thu, 23 Mar 2017, clinton.a.taylor@xxxxxxxxx wrote:
From: Clint Taylor <clinton.a.taylor@xxxxxxxxx>
Several major vendor USB-C->HDMI converters fail to recover a 5.4 GHz 1 lane
signal if the Data Link N is greater than 0x80000.
Patch detects when 1 lane 5.4 GHz signal is being used and makes the maximum
value 20 bit instead of the maximum specification supported 24 bit value.
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Anusha Srivatsa <anusha.srivatsa@xxxxxxxxx>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93578
I will add to the commit message.
Signed-off-by: Clint Taylor <clinton.a.taylor@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_reg.h | 2 ++
drivers/gpu/drm/i915/intel_display.c | 15 +++++++++++----
2 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 04c8f69..838d8d5 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -4869,6 +4869,8 @@ enum {
#define DATA_LINK_M_N_MASK (0xffffff)
#define DATA_LINK_N_MAX (0x800000)
+/* Maximum N value useable on some DP->HDMI converters */
+#define DATA_LINK_REDUCED_N_MAX (0x80000)
#define _PIPEA_DATA_N_G4X 0x70054
#define _PIPEB_DATA_N_G4X 0x71054
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 010e5dd..6e1fdd2 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6315,9 +6315,10 @@ static int intel_crtc_compute_config(struct intel_crtc *crtc,
}
static void compute_m_n(unsigned int m, unsigned int n,
- uint32_t *ret_m, uint32_t *ret_n)
+ uint32_t *ret_m, uint32_t *ret_n,
+ uint32_t max_link_n)
{
- *ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
+ *ret_n = min_t(unsigned int, roundup_pow_of_two(n), max_link_n);
If there's evidence suggesting "certain other operating systems" always
use a max (or fixed value) of 0x80000, perhaps we should just follow
suit? Simpler and less magical.
The other OS's don't appear to be fixed to 0x80000. The calculation in
i915 rounds up to the nearest power of 2 and the other OS's might have a
slightly different calculation to the nearest power of 2. Of course I
haven't seen the other OS's code to know their exact formula. HBR3 will
cause a higher value to be calculated and having a fixed value may cause
issues. The i915 formula works and reducing the value can cause
precision issues in the ratio with the pixel clock.
*ret_m = div_u64((uint64_t) m * *ret_n, n);
intel_reduce_m_n_ratio(ret_m, ret_n);
}
@@ -6327,14 +6328,20 @@ static void compute_m_n(unsigned int m, unsigned int n,
int pixel_clock, int link_clock,
struct intel_link_m_n *m_n)
{
+ uint32_t max_link_n = DATA_LINK_N_MAX;
m_n->tu = 64;
+ if ((nlanes==1) && (link_clock >= 540000))
Is the problem really dependent on these conditions? You can get the
same problematic N value with nlanes == 2 && link_clock == 270000 too.
The offending device only supports a single DP lane up to HBR2.5. This
check matches the datasheet for the part. The offending device works
with our current calculation at 1 lane HBR (270000).
Okay, so what bugs me about the approach here is that this adds an
arbitrary condition to apply a quirk to a specific device.
Instead of "if device X, then apply restriction A", this adds "if
condition Y, then apply restriction A". If I understand you correctly,
"condition Y" is a superset of "device X", i.e. Y happens also on
devices other than X, but on device X condition Y always holds.
I'd really like it if we could come up with a) a quirk that we apply
only on the affected device(s), or b) rules for M/N that generally make
sense with no need to resort to seeminly arbitrary exceptions.
I can detect the specific device through the DP OUI branch value
returned during DP detect. I can also detect through the device ID
string DPCD 0x503-0x508 currently not parsed in i915. Either would
satisfy Device X, Condition Y, then apply workaround A.
I would prefer a solution for B (rules for M/N), but the code doesn't
appear to be broken and I don't believe we should "Fix" something that
is working. The device also works by changing the roundup_pow_of_two()
to rounddown_pow_of_two() however that would apply the change to every
device connected.
With the latter I mean things like reducing the M/N before rounding N up
to power of two (M and N are always divisible by 2, for example) or
having intel_reduce_m_n_ratio() shift them right as long as they have
bit 0 unset. At a glance, I'm not sure if this is enough to bring down
the N to within the limits of the device, without intentional loss of
precision.
BR,
Jani.
BR,
Jani.
+ max_link_n = DATA_LINK_REDUCED_N_MAX;
+
compute_m_n(bits_per_pixel * pixel_clock,
link_clock * nlanes * 8,
- &m_n->gmch_m, &m_n->gmch_n);
+ &m_n->gmch_m, &m_n->gmch_n,
+ max_link_n);
compute_m_n(pixel_clock, link_clock,
- &m_n->link_m, &m_n->link_n);
+ &m_n->link_m, &m_n->link_n,
+ max_link_n);
}
static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)
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