On Mon, Sep 30, 2019 at 07:56:13AM -0400, Ilia Mirkin wrote:
On Mon, Sep 30, 2019 at 7:05 AM Brian Starkey Brian.Starkey@arm.com wrote:
Hi James,
On Mon, Sep 30, 2019 at 04:54:41AM +0000, james qian wang (Arm Technology China) wrote:
This function is used to convert drm_color_ctm S31.32 sign-magnitude value to komeda required Q2.12 2's complement
Signed-off-by: james qian wang (Arm Technology China) james.qian.wang@arm.com
.../arm/display/komeda/komeda_color_mgmt.c | 27 +++++++++++++++++++ .../arm/display/komeda/komeda_color_mgmt.h | 1 + 2 files changed, 28 insertions(+)
diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c index c180ce70c26c..c92c82eebddb 100644 --- a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c +++ b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c @@ -117,3 +117,30 @@ void drm_lut_to_fgamma_coeffs(struct drm_property_blob *lut_blob, u32 *coeffs) { drm_lut_to_coeffs(lut_blob, coeffs, sector_tbl, ARRAY_SIZE(sector_tbl)); }
+/* Convert from S31.32 sign-magnitude to HW Q2.12 2's complement */ +static s32 drm_ctm_s31_32_to_q2_12(u64 input) +{
u64 mag = (input & ~BIT_ULL(63)) >> 20;bool negative = !!(input & BIT_ULL(63));u32 val;/* the range of signed 2s complement is [-2^n, 2^n - 1] */val = clamp_val(mag, 0, negative ? BIT(14) : BIT(14) - 1);return negative ? 0 - val : val;+}
This function looks generally useful. Should it be in DRM core (assuming there isn't already one there)?
You can use a parameter to determine the number of bits desired in the output.
I suspect every driver needs to do something similar. You can see what I did for nouveau here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
(look for csc_drm_to_base)
Would be great to have a common helper which correctly accounts for all the variability.
Yeah the sign-bit 31.32 fixed point format is probably the most ludicrous uapi fumble we've ever done. A shared function, rolled out to drivers, to switch it to a signed 2 complements integer sounds like a _very_ good idea. -Daniel