Hi Pekka,
On Thu, Feb 10, 2022 at 6:50 AM Pekka Paalanen <ppaala...@gmail.com> wrote:
> On Fri, 21 Jan 2022 18:38:31 -0300
> Igor Torrente <igormtorre...@gmail.com> wrote:
>
> > Adds this common format to vkms.
> >
> > This commit also adds new helper macros to deal with fixed-point
> > arithmetic.
> >
> > It was done to improve the precision of the conversion to ARGB16161616
> > since the "conversion ratio" is not an integer.
> >
> > Signed-off-by: Igor Torrente <igormtorre...@gmail.com>
> > ---
> > V3: Adapt the handlers to the new format introduced in patch 7 V3.
> > ---
> > drivers/gpu/drm/vkms/vkms_formats.c | 74 +++++++++++++++++++++++++++
> > drivers/gpu/drm/vkms/vkms_formats.h | 6 +++
> > drivers/gpu/drm/vkms/vkms_plane.c | 6 ++-
> > drivers/gpu/drm/vkms/vkms_writeback.c | 3 +-
> > 4 files changed, 86 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vkms/vkms_formats.c
> b/drivers/gpu/drm/vkms/vkms_formats.c
> > index 661da39d1276..dc612882dd8c 100644
> > --- a/drivers/gpu/drm/vkms/vkms_formats.c
> > +++ b/drivers/gpu/drm/vkms/vkms_formats.c
> > @@ -11,6 +11,8 @@ format_transform_func get_fmt_transform_function(u32
> format)
> > return &get_ARGB16161616;
> > else if (format == DRM_FORMAT_XRGB16161616)
> > return &XRGB16161616_to_ARGB16161616;
> > + else if (format == DRM_FORMAT_RGB565)
> > + return &RGB565_to_ARGB16161616;
> > else
> > return &XRGB8888_to_ARGB16161616;
> > }
> > @@ -23,6 +25,8 @@ format_transform_func
> get_wb_fmt_transform_function(u32 format)
> > return &convert_to_ARGB16161616;
> > else if (format == DRM_FORMAT_XRGB16161616)
> > return &convert_to_XRGB16161616;
> > + else if (format == DRM_FORMAT_RGB565)
> > + return &convert_to_RGB565;
> > else
> > return &convert_to_XRGB8888;
> > }
> > @@ -33,6 +37,26 @@ static int pixel_offset(struct vkms_frame_info
> *frame_info, int x, int y)
> > + (x * frame_info->cpp);
> > }
> >
> > +/*
> > + * FP stands for _Fixed Point_ and **not** _Float Point_
>
> Is it common in the kernel that FP always means fixed-point?
>
I cannot say for sure, but I don't think so. I put it for people like me
that goes automatically to Floating-Point because never worked with
fixed-point before.
>
> If there is any doubt about that, I'd suggest using "fixed" and "float"
> to avoid misunderstandings.
>
> And, since you are not supposed to use floats in the kernel unless you
> really really must and you do all the preparations necessary (which you
> don't here), maybe replace the "float" with a fraction.
>
> In other words, write a macro that takes (65535, 31) as arguments
> instead of a float, when converting to fixed-point. Then you don't have
> to use those strange decimal constants either.
>
It looks better, I will try to implement this.
> > + * LF stands for Long Float (i.e. double)
> > + * The following macros help doing fixed point arithmetic.
> > + */
> > +/*
> > + * With FP scale 15 we have 17 and 15 bits of integer and fractional
> parts
> > + * respectively.
> > + * | 0000 0000 0000 0000 0.000 0000 0000 0000 |
> > + * 31 0
> > + */
> > +#define FP_SCALE 15
> > +
> > +#define LF_TO_FP(a) ((a) * (u64)(1 << FP_SCALE))
> > +#define INT_TO_FP(a) ((a) << FP_SCALE)
> > +#define FP_MUL(a, b) ((s32)(((s64)(a) * (b)) >> FP_SCALE))
> > +#define FP_DIV(a, b) ((s32)(((s64)(a) << FP_SCALE) / (b)))
> > +/* This macro converts a fixed point number to int, and round half up
> it */
> > +#define FP_TO_INT_ROUND_UP(a) (((a) + (1 << (FP_SCALE - 1))) >>
> FP_SCALE)
> > +
> > /*
> > * packed_pixels_addr - Get the pointer to pixel of a given pair of
> coordinates
> > *
> > @@ -125,6 +149,33 @@ void XRGB16161616_to_ARGB16161616(struct
> vkms_frame_info *frame_info, int y,
> > }
> > }
> >
> > +void RGB565_to_ARGB16161616(struct vkms_frame_info *frame_info, int y,
> > + struct line_buffer *stage_buffer)
> > +{
> > + u16 *src_pixels = get_packed_src_addr(frame_info, y);
> > + int x, x_limit = drm_rect_width(&frame_info->dst);
> > +
> > + for (x = 0; x < x_limit; x++, src_pixels++) {
> > + u16 rgb_565 = le16_to_cpu(*src_pixels);
> > + int fp_r = INT_TO_FP((rgb_565 >> 11) & 0x1f);
> > + int fp_g = INT_TO_FP((rgb_565 >> 5) & 0x3f);
> > + int fp_b = INT_TO_FP(rgb_565 & 0x1f);
> > +
> > + /*
> > + * The magic constants is the "conversion ratio" and is
> calculated
> > + * dividing 65535(2^16 - 1) by 31(2^5 -1) and 63(2^6 - 1)
> > + * respectively.
> > + */
> > + int fp_rb_ratio = LF_TO_FP(2114.032258065);
> > + int fp_g_ratio = LF_TO_FP(1040.238095238);
> > +
> > + stage_buffer[x].a = (u16)0xffff;
> > + stage_buffer[x].r = FP_TO_INT_ROUND_UP(FP_MUL(fp_r,
> fp_rb_ratio));
> > + stage_buffer[x].g = FP_TO_INT_ROUND_UP(FP_MUL(fp_g,
> fp_g_ratio));
> > + stage_buffer[x].b = FP_TO_INT_ROUND_UP(FP_MUL(fp_b,
> fp_rb_ratio));
> > + }
> > +}
> > +
> >
> > /*
> > * The following functions take an line of ARGB16161616 pixels from the
> > @@ -203,3 +254,26 @@ void convert_to_XRGB16161616(struct vkms_frame_info
> *frame_info, int y,
> > dst_pixels[0] = src_buffer[x].b;
> > }
> > }
> > +
> > +void convert_to_RGB565(struct vkms_frame_info *frame_info, int y,
> > + struct line_buffer *src_buffer)
> > +{
> > + int x, x_dst = frame_info->dst.x1;
> > + u16 *dst_pixels = packed_pixels_addr(frame_info, x_dst, y);
> > + int x_limit = drm_rect_width(&frame_info->dst);
> > +
> > + for (x = 0; x < x_limit; x++, dst_pixels++) {
> > + int fp_r = INT_TO_FP(src_buffer[x].r);
> > + int fp_g = INT_TO_FP(src_buffer[x].g);
> > + int fp_b = INT_TO_FP(src_buffer[x].b);
> > +
> > + int fp_rb_ratio = LF_TO_FP(2114.032258065);
> > + int fp_g_ratio = LF_TO_FP(1040.238095238);
>
> Are there any guarantees that this will not result in floating-point
> CPU instructions being used? Like a compiler error if it did?
>
> Yes, it's a constant expression, but I think there were some funny
> rules in C that floating-point operations may not be evaluated at
> compile time. Maybe I'm just paranoid?
>
>
Well, I cannot guarantee anything, but every time that I
intentionally/unintentionally
did anything related with floating-point it couldn't link the kernel.
>
> Thanks,
> pq
>
> > +
> > + u16 r = FP_TO_INT_ROUND_UP(FP_DIV(fp_r, fp_rb_ratio));
> > + u16 g = FP_TO_INT_ROUND_UP(FP_DIV(fp_g, fp_g_ratio));
> > + u16 b = FP_TO_INT_ROUND_UP(FP_DIV(fp_b, fp_rb_ratio));
> > +
> > + *dst_pixels = cpu_to_le16(r << 11 | g << 5 | b);
> > + }
> > +}
> > diff --git a/drivers/gpu/drm/vkms/vkms_formats.h
> b/drivers/gpu/drm/vkms/vkms_formats.h
> > index 22358f3a33ab..836d6e43ea90 100644
> > --- a/drivers/gpu/drm/vkms/vkms_formats.h
> > +++ b/drivers/gpu/drm/vkms/vkms_formats.h
> > @@ -21,6 +21,9 @@ void get_ARGB16161616(struct vkms_frame_info
> *frame_info, int y,
> > void XRGB16161616_to_ARGB16161616(struct vkms_frame_info *frame_info,
> int y,
> > struct line_buffer *stage_buffer);
> >
> > +void RGB565_to_ARGB16161616(struct vkms_frame_info *frame_info, int y,
> > + struct line_buffer *stage_buffer);
> > +
> > void convert_to_ARGB8888(struct vkms_frame_info *frame_info, int y,
> > struct line_buffer *src_buffer);
> >
> > @@ -33,6 +36,9 @@ void convert_to_ARGB16161616(struct vkms_frame_info
> *frame_info, int y,
> > void convert_to_XRGB16161616(struct vkms_frame_info *frame_info, int y,
> > struct line_buffer *src_buffer);
> >
> > +void convert_to_RGB565(struct vkms_frame_info *frame_info, int y,
> > + struct line_buffer *src_buffer);
> > +
> > typedef void (*format_transform_func)(struct vkms_frame_info
> *frame_info, int y,
> > struct line_buffer *buffer);
> >
> > diff --git a/drivers/gpu/drm/vkms/vkms_plane.c
> b/drivers/gpu/drm/vkms/vkms_plane.c
> > index 1d70c9e8f109..4643eefcdf29 100644
> > --- a/drivers/gpu/drm/vkms/vkms_plane.c
> > +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> > @@ -13,14 +13,16 @@
> >
> > static const u32 vkms_formats[] = {
> > DRM_FORMAT_XRGB8888,
> > - DRM_FORMAT_XRGB16161616
> > + DRM_FORMAT_XRGB16161616,
> > + DRM_FORMAT_RGB565
> > };
> >
> > static const u32 vkms_plane_formats[] = {
> > DRM_FORMAT_ARGB8888,
> > DRM_FORMAT_XRGB8888,
> > DRM_FORMAT_XRGB16161616,
> > - DRM_FORMAT_ARGB16161616
> > + DRM_FORMAT_ARGB16161616,
> > + DRM_FORMAT_RGB565
> > };
> >
> > static struct drm_plane_state *
> > diff --git a/drivers/gpu/drm/vkms/vkms_writeback.c
> b/drivers/gpu/drm/vkms/vkms_writeback.c
> > index 393d3fc7966f..1aaa630090d3 100644
> > --- a/drivers/gpu/drm/vkms/vkms_writeback.c
> > +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> > @@ -15,7 +15,8 @@
> > static const u32 vkms_wb_formats[] = {
> > DRM_FORMAT_XRGB8888,
> > DRM_FORMAT_XRGB16161616,
> > - DRM_FORMAT_ARGB16161616
> > + DRM_FORMAT_ARGB16161616,
> > + DRM_FORMAT_RGB565
> > };
> >
> > static const struct drm_connector_funcs vkms_wb_connector_funcs = {
>
>
