[Bug 29502] New: Change to legacy algo to preferring lower post dividers breaks certain modelines

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=29502

           Summary: Change to legacy algo to preferring lower post
                    dividers breaks certain modelines
           Product: Drivers
           Version: 2.5
    Kernel Version: 2.6.38-rc5
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
        AssignedTo: drivers_video-dri at kernel-bugs.osdl.org
        ReportedBy: bitbytebit at gmail.com
        Regression: Yes


There's an issue with some legacy chips plus low dotclocks in the 2.6.38-rc5
kernel, This is the change/patch that broke them.  Reverting this patch, they
work as they did before...

"Also, switch the legacy algo back to preferring lower post dividers."

@@ -849,7 +951,7 @@ void radeon_compute_pll(struct radeon_pll *pll,
         max_fractional_feed_div = pll->max_frac_feedback_div;
     }

-    for (post_div = max_post_div; post_div >= min_post_div; --post_div) {
+    for (post_div = min_post_div; post_div <= max_post_div; ++post_div) {
         uint32_t ref_div;

         if ((pll->flags & RADEON_PLL_NO_ODD_POST_DIV) && (post_div & 1))


A person has a ATI Radeon 9200SE 5964 (AGP)and with 2.6.38-rc4-git4+ it works
while with 2.6.38-rc5 there are certain (not all) modelines with low dotclocks
that end up being totally out of sync.

Here's an example of a non-working modeline for him with the newer kernel, vs.
the older one step back before the patch with the above change...


# toki 256x224 at 59.61 15.6774Khz
    ModeLine          "256x224x59.61" 5.518455 256 272 304 352 224 235 238 263
-HSync -VSync


There's a lot of other ones thought that can work with the same lower
dotclocks, so I'm not sure why that is, he tested that change with the legacy
pll computation reversed back to how it was and now works again with modelines
like the above.

Thanks,
Chris

-- 
Configure bugmail: https://bugzilla.kernel.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are watching the assignee of the bug.

------------------------------------------------------------------------------
The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE:
Pinpoint memory and threading errors before they happen.
Find and fix more than 250 security defects in the development cycle.
Locate bottlenecks in serial and parallel code that limit performance.
http://p.sf.net/sfu/intel-dev2devfeb
--
_______________________________________________
Dri-devel mailing list
Dri-devel at lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/dri-devel