[PATCH RFC 2/5] drm/msm: Add MSM-specific DSC helper methods

[Dmitry Baryshkov]

On 30/03/2023 02:18, Jessica Zhang wrote:
> Introduce MSM-specific DSC helper methods, as some calculations are
> common between DP and DSC.
> 
> Signed-off-by: Jessica Zhang <quic_jesszhan at quicinc.com>
> ---
>   drivers/gpu/drm/msm/Makefile              |  1 +
>   drivers/gpu/drm/msm/disp/msm_dsc_helper.c | 74 +++++++++++++++++++++++++++++++
>   drivers/gpu/drm/msm/disp/msm_dsc_helper.h | 28 ++++++++++++
>   3 files changed, 103 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> index 7274c41228ed..897a5b1c88f6 100644
> --- a/drivers/gpu/drm/msm/Makefile
> +++ b/drivers/gpu/drm/msm/Makefile
> @@ -90,6 +90,7 @@ msm-y += \
>   	disp/mdp_kms.o \
>   	disp/msm_disp_snapshot.o \
>   	disp/msm_disp_snapshot_util.o \
> +	disp/msm_dsc_helper.o \
>   	msm_atomic.o \
>   	msm_atomic_tracepoints.o \
>   	msm_debugfs.o \
> diff --git a/drivers/gpu/drm/msm/disp/msm_dsc_helper.c b/drivers/gpu/drm/msm/disp/msm_dsc_helper.c
> new file mode 100644
> index 000000000000..ec15c0d829e8
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/disp/msm_dsc_helper.c
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +#include <drm/drm_fixed.h>
> +
> +#include "msm_drv.h"
> +#include "msm_dsc_helper.h"
> +
> +static int get_comp_ratio(struct drm_dsc_config *dsc, u32 src_bpp)
> +{
> +	return mult_frac(100, src_bpp, DSC_BPP(*dsc));
> +}
> +
> +static s64 get_bytes_per_soft_slice(struct drm_dsc_config *dsc, int intf_width, int comp_ratio)
> +{
> +	s64 comp_ratio_fp, num_bits_fp;
> +	s64 numerator_fp, denominator_fp;
> +
> +	comp_ratio_fp = drm_fixp_from_fraction(comp_ratio, 100);

Please inline comp_ration calculation here. Don't use mult_frac().

> +	num_bits_fp = drm_fixp_from_fraction(8, 1);

drm_int2fixp

> +
> +	numerator_fp = drm_fixp_from_fraction(dsc->slice_width * dsc->bits_per_component * 3, 1);

And here too.

> +	denominator_fp = drm_fixp_mul(comp_ratio_fp, num_bits_fp);

And num_bits_fp can be inlined too.
denominator_fp = drm_fixp_from_fraction(src_bpp * 8, DSC_BPP)

> +
> +	return drm_fixp_div(numerator_fp, denominator_fp);

dsc->slice_width * bpc * 3 / (8 * src_bpp / DSC_BPP), thus:

drm_fixp_from_fraction(dsc->slice_width * bpc * 3 * DSC_BPP, 8 * src_bpp)

but I will not insist on this one.

> +}
> +
> +u32 msm_dsc_get_eol_byte_num(struct drm_dsc_config *dsc, int intf_width, u32 src_bpp)
> +{
> +	u32 bytes_per_ss, extra_eol_bytes, bytes_per_intf;
> +	s64 bytes_per_ss_fp;
> +	int slice_per_intf = msm_dsc_get_slice_per_intf(dsc, intf_width);
> +	int comp_ratio = get_comp_ratio(dsc, src_bpp);
> +
> +	bytes_per_ss_fp = get_bytes_per_soft_slice(dsc, intf_width, comp_ratio);
> +	bytes_per_ss = drm_fixp2int_ceil(bytes_per_ss_fp);

s/_ss/_soft_slice/g

> +
> +	bytes_per_intf = bytes_per_ss * slice_per_intf;
> +	extra_eol_bytes = bytes_per_intf % 3;
> +	if (extra_eol_bytes != 0)
> +		extra_eol_bytes = 3 - extra_eol_bytes;
> +
> +	return extra_eol_bytes;
> +}
> +
> +u32 msm_dsc_get_dce_bytes_per_line(struct drm_dsc_config *dsc, int intf_width)
> +{
> +	u32 bpp;
> +	u32 dce_bytes_per_line;
> +
> +	bpp = DSC_BPP(*dsc);

Didn't this cause a warning on the unused-but-set variable?

> +	dce_bytes_per_line = DIV_ROUND_UP(dsc->bits_per_pixel * intf_width, 8);
> +
> +	return dce_bytes_per_line;
> +}

If you have msm_dsc_get_slice_per_intf() as a static inline, this 
function can be a static inline too. Nothing more than a single 
DIV_ROUND_UP.

> +
> +int msm_dsc_get_pclk_per_line(struct drm_dsc_config *dsc, int intf_width, u32 src_bpp)
> +{
> +	s64 data_width;
> +	int comp_ratio = get_comp_ratio(dsc, src_bpp);
> +
> +	if (!dsc->slice_width || (intf_width < dsc->slice_width))
> +		return -EINVAL;
> +
> +	data_width = get_bytes_per_soft_slice(dsc, intf_width, comp_ratio);
> +	data_width = drm_fixp_mul(dsc->slice_count, data_width);
> +	data_width = drm_fixp_from_fraction(data_width, 3);

Reusing a variable is a nice trick, but it can be confusing. Not to 
mention that the last call should probably be drm_fixp_div()

> +
> +	return drm_fixp2int_ceil(data_width);
> +}
> diff --git a/drivers/gpu/drm/msm/disp/msm_dsc_helper.h b/drivers/gpu/drm/msm/disp/msm_dsc_helper.h
> new file mode 100644
> index 000000000000..308069b2b5a4
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/disp/msm_dsc_helper.h
> @@ -0,0 +1,28 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved
> + */
> +
> +#ifndef MSM_DSC_HELPER_H_
> +#define MSM_DSC_HELPER_H_
> +
> +#include <drm/display/drm_dsc_helper.h>
> +#include <drm/drm_modes.h>
> +
> +/*
> + * Helper methods for MSM specific DSC calculations that are common between timing engine,
> + * DSI, and DP.
> + */
> +
> +#define MSM_DSC_SLICE_PER_PKT 1
> +#define DSC_BPP(config) ((config).bits_per_pixel >> 4)

Oh. Please. If you have used (config)->bits_per_pixel here, you wouldn't 
have to use clumsy DSC_BPP(*dsc). It might make sense to add:

static inline drm_dsc_get_bpp_int(struct drm_dsc_config *dsc)
{
     // most probably WARN_ON_ONCE is enough.
     WARN_ON(dsc->bits_per_fixel & 0xf);

     return dsc->bits_per_pixel >> 4;
}

> +
> +static inline int msm_dsc_get_slice_per_intf(struct drm_dsc_config *dsc, int intf_width)
> +{
> +	return DIV_ROUND_UP(intf_width, dsc->slice_width);
> +}
> +
> +u32 msm_dsc_get_eol_byte_num(struct drm_dsc_config *dsc, int intf_width, u32 src_bpp);
> +u32 msm_dsc_get_dce_bytes_per_line(struct drm_dsc_config *dsc, int intf_width);
> +int msm_dsc_get_pclk_per_line(struct drm_dsc_config *dsc, int intf_width, u32 src_bpp);
> +#endif /* MSM_DSC_HELPER_H_ */
> 

-- 
With best wishes
Dmitry