Re: [PATCH v10 2/2] drm: add kms driver for loongson display controller

[Emil Velikov]

Greetings Sui Jingfeng,

I haven't been around drm-land for a while and this is the first
driver I skim through in a few years. So take the following
suggestions with a healthy pinch of salt.

Hope that helps o/

On Mon, 3 Apr 2023 at 18:13, Sui Jingfeng <suijingfeng@xxxxxxxxxxx> wrote:

>   v7 -> v8:
>    1) Zero a compile warnnings on 32-bit platform, compile with W=1
>    2) Revise lsdc_bo_gpu_offset() and minor cleanup
>    3) Pageflip tested on the virtual terminal with following commands
>
>       modetest -M loongson -s 32:1920x1080 -v
>       modetest -M loongson -s 34:1920x1080 -v -F tiles
>

I could be wrong, but my understanding is that new drivers should be
capable of running under Xorg and/or Wayland compositor. There is also
the IGT test suite, which can help verify and validate the driver's
behaviour:

https://www.kernel.org/doc/html/latest/gpu/drm-uapi.html



> +static void lsdc_crtc_reset(struct drm_crtc *crtc)
> +{
> +       struct lsdc_display_pipe *dispipe = crtc_to_display_pipe(crtc);
> +       struct drm_device *ddev = crtc->dev;
> +       struct lsdc_device *ldev = to_lsdc(ddev);
> +       struct lsdc_crtc_state *priv_crtc_state;
> +       unsigned int index = dispipe->index;
> +       u32 val;
> +
> +       val = LSDC_PF_XRGB8888 | CFG_RESET_N;
> +       if (ldev->descp->chip == CHIP_LS7A2000)
> +               val |= LSDC_DMA_STEP_64_BYTES;
> +
> +       lsdc_crtc_wreg32(ldev, LSDC_CRTC0_CFG_REG, index, val);
> +
> +       if (ldev->descp->chip == CHIP_LS7A2000) {
> +               val = PHY_CLOCK_EN | PHY_DATA_EN;
> +               lsdc_crtc_wreg32(ldev, LSDC_CRTC0_PANEL_CONF_REG, index, val);
> +       }
> +

AFAICT no other driver touches the HW in their reset callback. Should
the above be moved to another callback?



> +static void lsdc_crtc_atomic_enable(struct drm_crtc *crtc,
> +                                   struct drm_atomic_state *state)
> +{

> +       val = lsdc_crtc_rreg32(ldev, LSDC_CRTC0_CFG_REG, index);
> +       /* clear old dma step settings */
> +       val &= ~CFG_DMA_STEP_MASK;
> +
> +       if (descp->chip == CHIP_LS7A2000) {
> +               /*
> +                * Using large dma step as much as possible,
> +                * for improve hardware DMA efficiency.
> +                */
> +               if (width_in_bytes % 256 == 0)
> +                       val |= LSDC_DMA_STEP_256_BYTES;
> +               else if (width_in_bytes % 128 == 0)
> +                       val |= LSDC_DMA_STEP_128_BYTES;
> +               else if (width_in_bytes % 64 == 0)
> +                       val |= LSDC_DMA_STEP_64_BYTES;
> +               else  /* width_in_bytes % 32 == 0 */
> +                       val |= LSDC_DMA_STEP_32_BYTES;
> +       }
> +
> +       clk_func->update(pixpll, &priv_state->pparms);
> +

Without knowing the hardware, the clk_func abstraction seems quite
arbitrary and unnecessary. It should be introduced when there is a
use-case for it.


> +       lsdc_crtc_wreg32(ldev, LSDC_CRTC0_CFG_REG, index, val | CFG_OUTPUT_EN);
> +
> +       drm_crtc_vblank_on(crtc);
> +}
> +


> --- /dev/null
> +++ b/drivers/gpu/drm/loongson/lsdc_debugfs.c

> +void lsdc_debugfs_init(struct drm_minor *minor)
> +{
> +#ifdef CONFIG_DEBUG_FS
> +       drm_debugfs_create_files(lsdc_debugfs_list,
> +                                ARRAY_SIZE(lsdc_debugfs_list),
> +                                minor->debugfs_root,
> +                                minor);
> +#endif
> +}

Should probably build the file when debugfs is enabled and provide
no-op stub in the header. See nouveau for an example.


> --- /dev/null
> +++ b/drivers/gpu/drm/loongson/lsdc_drv.c

> +static const struct lsdc_desc dc_in_ls7a1000 = {
> +       .chip = CHIP_LS7A1000,
> +       .num_of_crtc = LSDC_NUM_CRTC,
> +       .max_pixel_clk = 200000,
> +       .max_width = 2048,
> +       .max_height = 2048,
> +       .num_of_hw_cursor = 1,
> +       .hw_cursor_w = 32,
> +       .hw_cursor_h = 32,
> +       .pitch_align = 256,
> +       .mc_bits = 40,
> +       .has_vblank_counter = false,
> +       .has_scan_pos = true,
> +       .has_builtin_i2c = true,
> +       .has_vram = true,
> +       .has_hpd_reg = false,
> +       .is_soc = false,
> +};
> +
> +static const struct lsdc_desc dc_in_ls7a2000 = {
> +       .chip = CHIP_LS7A2000,
> +       .num_of_crtc = LSDC_NUM_CRTC,
> +       .max_pixel_clk = 350000,
> +       .max_width = 4096,
> +       .max_height = 4096,
> +       .num_of_hw_cursor = 2,
> +       .hw_cursor_w = 64,
> +       .hw_cursor_h = 64,
> +       .pitch_align = 64,
> +       .mc_bits = 40, /* support 48, but use 40 for backward compatibility */
> +       .has_vblank_counter = true,
> +       .has_scan_pos = true,
> +       .has_builtin_i2c = true,
> +       .has_vram = true,
> +       .has_hpd_reg = true,
> +       .is_soc = false,
> +};
> +

Roughly a quarter of the above are identical. It might be better to
drop them for now and re-introduce as needed with future code.

> +const char *chip_to_str(enum loongson_chip_family chip)
> +{
> +       if (chip == CHIP_LS7A2000)
> +               return "LS7A2000";
> +
> +       if (chip == CHIP_LS7A1000)
> +               return "LS7A1000";
> +

If it were me, I would add the name into the lsdc_desc.


> +static enum drm_mode_status
> +lsdc_mode_config_mode_valid(struct drm_device *ddev,
> +                           const struct drm_display_mode *mode)
> +{
> +       struct lsdc_device *ldev = to_lsdc(ddev);
> +       const struct drm_format_info *info = drm_format_info(DRM_FORMAT_XRGB8888);

Short-term hard coding a format is fine, but there should be a comment
describing why.

> +       u64 min_pitch = drm_format_info_min_pitch(info, 0, mode->hdisplay);
> +       u64 fb_size = min_pitch * mode->vdisplay;
> +
> +       if (fb_size * 3 > ldev->vram_size) {

Why are we using 3 here? Please add an inline comment.


> +static const struct dev_pm_ops lsdc_pm_ops = {
> +       .suspend = lsdc_pm_suspend,
> +       .resume = lsdc_pm_resume,
> +       .freeze = lsdc_pm_freeze,
> +       .thaw = lsdc_pm_thaw,
> +       .poweroff = lsdc_pm_freeze,
> +       .restore = lsdc_pm_resume,
> +};
> +

The above section (and functions) should probably be wrapped in a
CONFIG_PM_SLEEP block.



> +static const struct pci_device_id lsdc_pciid_list[] = {
> +       {PCI_VENDOR_ID_LOONGSON, 0x7a06, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CHIP_LS7A1000},
> +       {PCI_VENDOR_ID_LOONGSON, 0x7a36, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CHIP_LS7A2000},
> +       {0, 0, 0, 0, 0, 0, 0}
> +};
> +

> +static int __init loongson_module_init(void)
> +{

> +       while ((pdev = pci_get_class(PCI_CLASS_DISPLAY_VGA << 8, pdev))) {
> +               if (pdev->vendor != PCI_VENDOR_ID_LOONGSON) {
> +                       pr_info("Discrete graphic card detected, abort\n");
> +                       return 0;
> +               }
> +       }

You can set the class/class_mask in the lsdc_pciid_list and drop this
loop. The vendor is already listed above and checked by core.



> +++ b/drivers/gpu/drm/loongson/lsdc_drv.h
> @@ -0,0 +1,324 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2022 Loongson Corporation
> + *

We're in 2023, update the year across the files?



> +struct lsdc_gem {
> +       /* @mutex: protect objects list */
> +       struct mutex mutex;
> +       struct list_head objects;
> +};
> +

> +struct lsdc_device {
> +       struct drm_device base;
> +       struct ttm_device bdev;
> +
> +       /* @descp: features description of the DC variant */
> +       const struct lsdc_desc *descp;
> +
> +       struct pci_dev *gpu;
> +
> +       /* @reglock: protects concurrent access */
> +       spinlock_t reglock;
> +       void __iomem *reg_base;
> +       resource_size_t vram_base;
> +       resource_size_t vram_size;
> +
> +       resource_size_t gtt_size;
> +
> +       struct lsdc_display_pipe dispipe[LSDC_NUM_CRTC];
> +
> +       struct lsdc_gem gem;
> +

Last time I looked there was no other driver with a list of gem
objects (and a mutex) in its device struct. Are you sure we need this?

Very few drivers use TTM directly and I think you want to use
drm_gem_vram_helper or drm_gem_ttm_helper instead.



> +static int ls7a1000_pixpll_param_update(struct lsdc_pll * const this,
> +                                       struct lsdc_pll_parms const *pin)
> +{
> +       void __iomem *reg = this->mmio;
> +       unsigned int counter = 0;
> +       bool locked;
> +       u32 val;
> +
> +       /* Bypass the software configured PLL, using refclk directly */
> +       val = readl(reg + 0x4);
> +       val &= ~(1 << 8);
> +       writel(val, reg + 0x4);
> +

There are a lot of magic numbers in this function. Let's define them
properly in the header.



> +/* Helpers for chip detection */
> +bool lsdc_is_ls2k2000(void);
> +bool lsdc_is_ls2k1000(void);
> +unsigned int loongson_cpu_get_prid(u8 *impl, u8 *rev);


Since this revision does pci_devices only, we don't need this detection right?


Hope that helps,
Emil