Hi,
On 20 May 2015 at 17:31, Tobias Jakobi tjakobi@math.uni-bielefeld.de wrote:
On 2015-05-20 18:14, Daniel Stone wrote:
On 20 May 2015 at 17:04, Tobias Jakobi tjakobi@math.uni-bielefeld.de wrote:
I wonder if that really 'fixes' anything, because now we get a WARN_ON which is immediately followed by a div-by-zero. Furthermore we then still use the result of that operation as input for a hw register (bad idea?)
I thought of something like this. Change fimd_calc_clkdiv() to return a signed value (this shouldn't be a problem, since the returned number range is small anywary). Let fimd_calc_clkdiv() return -1 when it encounters the 'ideal_clk == 0' case. Move computation of clkdiv in fimd_commit() to the top of the function (right after the {h,v}total checks). If 'clkdiv == -1' case is encountered, then do WARN_ON and return immediately from fimd_commit().
Should I prepare a patch for this, or does someone see an issue with this approach?
Commit should never fail; as I said earlier, the right fix is to reject these modes during checking, by making sure that any mode which passes mode_fixup() and/or mode_valid() never trips this condition.
But then in this case it wouldn't help to call drm_mode_vrefresh() during fixup, since it still returns zero, so we're in the same situation as before.
fixup can reject a mode entirely by returning false, which is the sane thing to do here if the clock is zero.
I even wonder if fixup is doing anything at all. See my previous log in: http://www.spinics.net/lists/linux-samsung-soc/msg44683.html
This is with the old code in fixup that should set vrefresh to 60.
And we see that it's actually called: [ 135.978878] [drm:fimd_mode_fixup] vrefresh 0
But then a small while later: [ 135.979048] [drm:fimd_calc_clkdiv] vrefresh 0
So apparantly nothing was fixed up here anyway?!
Ah. That would be because fimd_calc_clkdiv uses &crtc->base.mode (passed by fimd_commit), instead of crtc->state->adjusted_mode. Does making that change help?
Cheers, Daniel