[RFC PATCH 1/4] drm/msm/mdss: convert UBWC setup to use match data

[Marijn Suijten]

On 2023-01-09 12:32:18, Abhinav Kumar wrote:
<snip>
> >> On 12/7/2022 4:08 PM, Dmitry Baryshkov wrote:
<snip>
> >>> +struct msm_mdss_data {
> >>> +    u32 ubwc_version;
> >>> +    u32 ubwc_swizzle;
> >>> +    u32 ubwc_static;
> >>> +    u32 highest_bank_bit;
> >>> +    u32 macrotile_mode;
> >>> +};

This magic struct could really use some documentation, otherwise users
will have no idea what fields to set (or omit) nor what values to use.
For example decoder 2.0 seems to only use ubwc_static as a sort of magic
"we don't know what the bits in UBWC_STATIC mean", whereas decoder 3.0
reconstructs this field entirely from the other parameters.  Decoder 4.0
however does the same, but _also_ embeds this uwbc_static magic value
back into the register value....?

Also read on below about checking "compatibility" between this struct
and the decoder version, and why I feel this struct (versus mandatory
function arguments) makes this struct less robust.

> >>>   struct msm_mdss {
> >>>       struct device *dev;
> >>> @@ -40,6 +48,7 @@ struct msm_mdss {
> >>>           unsigned long enabled_mask;
> >>>           struct irq_domain *domain;
> >>>       } irq_controller;
> >>> +    const struct msm_mdss_data *mdss_data;
> >>>       struct icc_path *path[2];
> >>>       u32 num_paths;
> >>>   };
> >>> @@ -180,46 +189,40 @@ static int _msm_mdss_irq_domain_add(struct 
> >>> msm_mdss *msm_mdss)
> >>>   #define UBWC_3_0 0x30000000
> >>>   #define UBWC_4_0 0x40000000
> >>> -static void msm_mdss_setup_ubwc_dec_20(struct msm_mdss *msm_mdss,
> >>> -                       u32 ubwc_static)
> >>> +static void msm_mdss_setup_ubwc_dec_20(struct msm_mdss *msm_mdss)
> >>>   {
> >>> -    writel_relaxed(ubwc_static, msm_mdss->mmio + UBWC_STATIC);
> >>> +    const struct msm_mdss_data *data = msm_mdss->mdss_data;
> >>> +
> >>> +    writel_relaxed(data->ubwc_static, msm_mdss->mmio + UBWC_STATIC);
> >>>   }
> >>> -static void msm_mdss_setup_ubwc_dec_30(struct msm_mdss *msm_mdss,
> >>> -                       unsigned int ubwc_version,
> >>> -                       u32 ubwc_swizzle,
> >>> -                       u32 highest_bank_bit,
> >>> -                       u32 macrotile_mode)
> >>> +static void msm_mdss_setup_ubwc_dec_30(struct msm_mdss *msm_mdss)
> >>>   {
> >>> -    u32 value = (ubwc_swizzle & 0x1) |
> >>> -            (highest_bank_bit & 0x3) << 4 |
> >>> -            (macrotile_mode & 0x1) << 12;
> >>> +    const struct msm_mdss_data *data = msm_mdss->mdss_data;
> >>> +    u32 value = (data->ubwc_swizzle & 0x1) |
> >>> +            (data->highest_bank_bit & 0x3) << 4 |
> >>> +            (data->macrotile_mode & 0x1) << 12;
> >>> -    if (ubwc_version == UBWC_3_0)
> >>> +    if (data->ubwc_version == UBWC_3_0)
> >>>           value |= BIT(10);
> >>> -    if (ubwc_version == UBWC_1_0)
> >>> +    if (data->ubwc_version == UBWC_1_0)
> >>>           value |= BIT(8);
> >>>       writel_relaxed(value, msm_mdss->mmio + UBWC_STATIC);
> >>>   }
> >>> -static void msm_mdss_setup_ubwc_dec_40(struct msm_mdss *msm_mdss,
> >>> -                       unsigned int ubwc_version,
> >>> -                       u32 ubwc_swizzle,
> >>> -                       u32 ubwc_static,
> >>> -                       u32 highest_bank_bit,
> >>> -                       u32 macrotile_mode)
> >>> +static void msm_mdss_setup_ubwc_dec_40(struct msm_mdss *msm_mdss)
> >>>   {
> >>> -    u32 value = (ubwc_swizzle & 0x7) |
> >>> -            (ubwc_static & 0x1) << 3 |
> >>> -            (highest_bank_bit & 0x7) << 4 |
> >>> -            (macrotile_mode & 0x1) << 12;
> >>> +    const struct msm_mdss_data *data = msm_mdss->mdss_data;
> >>> +    u32 value = (data->ubwc_swizzle & 0x7) |
> >>> +            (data->ubwc_static & 0x1) << 3 |
> >>> +            (data->highest_bank_bit & 0x7) << 4 |
> >>> +            (data->macrotile_mode & 0x1) << 12;
> >>>       writel_relaxed(value, msm_mdss->mmio + UBWC_STATIC);
> >>> -    if (ubwc_version == UBWC_3_0) {
> >>> +    if (data->ubwc_version == UBWC_3_0) {
> >>>           writel_relaxed(1, msm_mdss->mmio + UBWC_CTRL_2);
> >>>           writel_relaxed(0, msm_mdss->mmio + UBWC_PREDICTION_MODE);
> >>>       } else {
> >>> @@ -232,6 +235,7 @@ static int msm_mdss_enable(struct msm_mdss 
> >>> *msm_mdss)
> >>>   {
> >>>       int ret;
> >>>       u32 hw_rev;
> >>> +    u32 ubwc_dec_hw_version;
> >>>       /*
> >>>        * Several components have AXI clocks that can only be turned 
> >>> on if
> >>> @@ -250,53 +254,36 @@ static int msm_mdss_enable(struct msm_mdss 
> >>> *msm_mdss)
> >>>        * HW_REV requires MDSS_MDP_CLK, which is not enabled by the 
> >>> mdss on
> >>>        * mdp5 hardware. Skip reading it for now.
> >>>        */
> >>> -    if (msm_mdss->is_mdp5)
> >>> +    if (msm_mdss->is_mdp5 || !msm_mdss->mdss_data)
> >>>           return 0;
> >>>       hw_rev = readl_relaxed(msm_mdss->mmio + HW_REV);
> 
> hw_rev is not used anymore now so why not just drop that reg read 
> altogether.
> 
> >>>       dev_dbg(msm_mdss->dev, "HW_REV: 0x%x\n", hw_rev);
> >>> +
> >>> +    ubwc_dec_hw_version = readl_relaxed(msm_mdss->mmio + 
> >>> UBWC_DEC_HW_VERSION);
> 
> If we are going to tie UBWC version to the HW compatible match, then 
> even this register read can be skipped and instead you can add 
> ubwc_dec_hw_version to your match data struct and skip this read as well.

I have suggested in IRC to keep this register read, and utilize it to at
least sanity check the configuration.  You are right that the DPU HW
version already describes what UWBC decoder version is used, but we're
are already questioning whether it was ported correctly for SM6115.  A
WARN() that catches a mismatch between what was written in the "catalog"
(or this match table) versus what the hardware reports would have gone a
long way.

This is especially relevant with the new struct where fields are
(un)used depending on the UBWC HW decoder version, making for an extra
exercise to the developer to double-check whether their struct values
are taken into account or not (or if used ones are accidentally
omitted).

- Marijn

> That way we get rid of all register reads in this path which have 
> continuously bugged us with crashes.

<snip>