Re: [PATCH RFC v2 2/6] drm/msm: Add MSM-specific DSC helper methods

[Jessica Zhang <quic_jesszhan@quicinc.com>]

On 4/2/2023 4:21 AM, Dmitry Baryshkov wrote:
> On 31/03/2023 21:49, Jessica Zhang wrote:
>> Introduce MSM-specific DSC helper methods, as some calculations are
>> common between DP and DSC.
>>
>> Changes in v2:
>> - Moved files up to msm/ directory
>> - Dropped get_comp_ratio() helper
>> - Used drm_int2fixp() to convert to integers to fp
>> - Style changes to improve readability
>> - Dropped unused bpp variable in msm_dsc_get_dce_bytes_per_line()
>> - Changed msm_dsc_get_slice_per_intf() to a static inline method
>> - Dropped last division step of msm_dsc_get_pclk_per_line() and changed
>>    method name accordingly
>> - Changed DSC_BPP macro to drm_dsc_get_bpp_int() helper method
>> - Fixed some math issues caused by passing in incorrect types to
>>    drm_fixed methods in get_bytes_per_soft_slice()
>>
>> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
>> ---
>>   drivers/gpu/drm/msm/Makefile         |  1 +
>>   drivers/gpu/drm/msm/msm_dsc_helper.c | 53 
>> ++++++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/msm/msm_dsc_helper.h | 42 ++++++++++++++++++++++++++++
>>   3 files changed, 96 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
>> index 7274c41228ed..b814fc80e2d5 100644
>> --- a/drivers/gpu/drm/msm/Makefile
>> +++ b/drivers/gpu/drm/msm/Makefile
>> @@ -94,6 +94,7 @@ msm-y += \
>>       msm_atomic_tracepoints.o \
>>       msm_debugfs.o \
>>       msm_drv.o \
>> +    msm_dsc_helper.o \
>>       msm_fb.o \
>>       msm_fence.o \
>>       msm_gem.o \
>> diff --git a/drivers/gpu/drm/msm/msm_dsc_helper.c 
>> b/drivers/gpu/drm/msm/msm_dsc_helper.c
>> new file mode 100644
>> index 000000000000..60b73e17e6eb
>> --- /dev/null
>> +++ b/drivers/gpu/drm/msm/msm_dsc_helper.c
>> @@ -0,0 +1,53 @@
>> +// 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 s64 get_bytes_per_soft_slice(struct drm_dsc_config *dsc, int 
>> intf_width, u32 src_bpp)
> 
> intf_width is unused

Hi Dmitry,

Acked.

> 
>> +{
>> +    int bpp = msm_dsc_get_bpp_int(dsc);
>> +    s64 numerator_fp, denominator_fp;
>> +    s64 comp_ratio_fp = drm_fixp_from_fraction(src_bpp, bpp);
>> +
>> +    numerator_fp = drm_int2fixp(dsc->slice_width * 3);
> 
> You have lost dsc->bits_per_component here.

This was moved to the denominator calculation, but I'll move it back to 
this line to avoid confusion.

> 
>> +    denominator_fp = drm_fixp_from_fraction(comp_ratio_fp * 8, 
>> drm_int2fixp(bpp));
> 
> denominator_fp = drm_fixp_from_fraction(src_bpp * 8, bpp);

Acked.

> 
>> +
>> +    return drm_fixp_div(numerator_fp, denominator_fp);
>> +}
>> +
>> +u32 msm_dsc_get_eol_byte_num(struct drm_dsc_config *dsc, int 
>> intf_width, u32 src_bpp)
>> +{
>> +    u32 bytes_per_soft_slice, extra_eol_bytes, bytes_per_intf;
>> +    s64 bytes_per_soft_slice_fp;
>> +    int slice_per_intf = msm_dsc_get_slice_per_intf(dsc, intf_width);
>> +
>> +    bytes_per_soft_slice_fp = get_bytes_per_soft_slice(dsc, 
>> intf_width, src_bpp);
>> +    bytes_per_soft_slice = drm_fixp2int_ceil(bytes_per_soft_slice_fp);
>> +
>> +    bytes_per_intf = bytes_per_soft_slice * slice_per_intf;
>> +    extra_eol_bytes = bytes_per_intf % 3;
>> +    if (extra_eol_bytes != 0)
>> +        extra_eol_bytes = 3 - extra_eol_bytes;
> 
> I become confused here when I checked eol_bytes in the display techpack.
> 
> I see that for DP the dp_panel_dsc_pclk_param_calc() calculates 
> dsc->eol_bytes_num in this way, the size to pad dsc_byte_count * 
> slice_per_intf to 3 bytes.
> 
> However, for DSI this is a simple as total_bytes_per_intf % 3 , so it is 
> not a padding, but a length of the last chunk.
> 
> Could you please clarify? If the techpack code is correct, I'd prefer if 
> we return last chunk size here and calculate the padding length in the 
> DP driver.

I've double checked the calculations between DP and DSI, and I think 
you're right. Will move the `if (extra_eol_bytes != 0)` block out to DP 
code.

> 
>> +
>> +    return extra_eol_bytes;
>> +}
>> +
>> +int msm_dsc_get_uncompressed_pclk_per_line(struct drm_dsc_config 
>> *dsc, int intf_width, u32 src_bpp)
> 
> Basing on Abhinav's description ("pclk_per_line can be only per 
> interface") would it better be named as 
> msm_dsc_get_uncompressed_pclk_per_intf() ? or 
> msm_dsc_get_uncompressed_pclk_for_intf() ?
> 
> BTW: if get_bytes_per_soft_slice() doesn't use intf_width, we can 
> probably drop it here too.
> 
>> +{
>> +    s64 data_width;
>> +
>> +    if (!dsc->slice_width || (intf_width < dsc->slice_width))
>> +        return -EINVAL;
> 
> Error code is not validated at dsi_timing_setup. I'd suggest moving 
> error checks there and dropping the error handling here. If 
> dsc->slice_width is not set, we should stop much earlier than 
> drm_bridge's pre_enable() callback.

Acked.

Thanks,

Jessica Zhang

> 
>> +
>> +    data_width = drm_fixp_mul(dsc->slice_count,
>> +            get_bytes_per_soft_slice(dsc, intf_width, src_bpp));
>> +
>> +    return drm_fixp2int_ceil(data_width);
>> +}
>> diff --git a/drivers/gpu/drm/msm/msm_dsc_helper.h 
>> b/drivers/gpu/drm/msm/msm_dsc_helper.h
>> new file mode 100644
>> index 000000000000..743cd324b7d9
>> --- /dev/null
>> +++ b/drivers/gpu/drm/msm/msm_dsc_helper.h
>> @@ -0,0 +1,42 @@
>> +/* 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.
>> + */
>> +
>> +static inline int msm_dsc_get_bpp_int(struct drm_dsc_config *dsc)
>> +{
>> +    WARN_ON_ONCE(dsc->bits_per_pixel & 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);
>> +}
>> +
>> +static inline u32 msm_dsc_get_dce_bytes_per_line(struct 
>> drm_dsc_config *dsc, int intf_width)
>> +{
>> +    return DIV_ROUND_UP(msm_dsc_get_bpp_int(dsc) * intf_width, 8);
>> +}
>> +
>> +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);
>> +
>> +/* Calculate uncompressed pclk per line. This value will then be 
>> passed along to
>> + * DSI and DP to calculate pclk_per_line. This is because DSI and DP 
>> divide the
>> + * uncompressed pclk_per_line by different values depending on if 
>> widebus is enabled.
>> + */
>> +int msm_dsc_get_uncompressed_pclk_per_line(struct drm_dsc_config *dsc,
>> +        int intf_width, u32 src_bpp);
>> +#endif /* MSM_DSC_HELPER_H_ */
>>
> 
> -- 
> With best wishes
> Dmitry
>