drm/msm: Add MSM-specific DSC helper methods

Introduce MSM-specific DSC helper methods, as some calculations are
common between DP and DSC.

Reviewed-by: Marijn Suijten <[e-mail]>
Signed-off-by: Jessica Zhang <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/539272/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/msm/msm_dsc_helper.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved
+ *
+ * Helper methods for MSM-specific DSC calculations that are common between timing engine,
+ * DSI, and DP.
+ */
+
+#ifndef MSM_DSC_HELPER_H_
+#define MSM_DSC_HELPER_H_
+
+#include <linux/math.h>
+#include <drm/display/drm_dsc_helper.h>
+
+/**
+ * msm_dsc_get_slices_per_intf() - calculate number of slices per interface
+ * @dsc: Pointer to drm dsc config struct
+ * @intf_width: interface width in pixels
+ * Returns: Integer representing the number of slices for the given interface
+ */
+static inline u32 msm_dsc_get_slices_per_intf(const struct drm_dsc_config *dsc, u32 intf_width)
+{
+	return DIV_ROUND_UP(intf_width, dsc->slice_width);
+}
+
+/**
+ * msm_dsc_get_bytes_per_line() - calculate bytes per line
+ * @dsc: Pointer to drm dsc config struct
+ * Returns: Integer value representing bytes per line. DSI and DP need
+ *          to perform further calculations to turn this into pclk_per_intf,
+ *          such as dividing by different values depending on if widebus is enabled.
+ */
+static inline u32 msm_dsc_get_bytes_per_line(const struct drm_dsc_config *dsc)
+{
+	return dsc->slice_count * dsc->slice_chunk_size;
+}
+
+#endif /* MSM_DSC_HELPER_H_ */