Re: [Intel-gfx] [PATCH v3 08/22] drm/i915/bios: Generate LFP data table pointers if the VBT lacks them

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 06 Apr 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Modern VBTs no longer contain the LFP data table pointers
> block (41). We are expecting to have one in order to be able
> to parse the LFP data block (42), so let's make one up.
>
> Since the fp_timing table has variable size we must somehow
> determine its size. Rather than just hardcode it we look for
> the terminator bytes (0xffff) to figure out where each table
> entry starts. dvo_timing, panel_pnp_id, and panel_name are
> expected to have fixed size.
>
> This has been observed on various machines, eg. TGL with BDB
> version 240, CML with BDB version 231, etc. The most recent
> VBT I've observed that still had block 41 had BDB version
> 228. So presumably the cutoff (if an exact cutoff even exists)
> is somewhere around BDB version 229-231.
>
> v2: kfree the thing we allocated, not the thing+3 bytes
> v3: Do the debugprint only if we found the LFP data block
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 136 +++++++++++++++++++++-
>  1 file changed, 135 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index 8b118c54314d..d32091dad1b0 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -310,16 +310,146 @@ static bool fixup_lfp_data_ptrs(const void *bdb, void *ptrs_block)
>  	return validate_lfp_data_ptrs(bdb, ptrs);
>  }
>  
> +static const void *find_fp_timing_terminator(const u8 *data, int size)
> +{
> +	int i;
> +
> +	if (!data)
> +		return NULL;
> +
> +	for (i = 0; i < size - 1; i++) {
> +		if (data[i] == 0xff && data[i+1] == 0xff)
> +			return &data[i];
> +	}
> +
> +	return NULL;
> +}
> +
> +static int make_lfp_data_ptr(struct lvds_lfp_data_ptr_table *table,
> +			     int table_size, int total_size)
> +{
> +	if (total_size < table_size)
> +		return total_size;
> +
> +	table->table_size = table_size;
> +	table->offset = total_size - table_size;
> +
> +	return total_size - table_size;
> +}
> +
> +static void next_lfp_data_ptr(struct lvds_lfp_data_ptr_table *next,
> +			      const struct lvds_lfp_data_ptr_table *prev,
> +			      int size)
> +{
> +	next->table_size = prev->table_size;
> +	next->offset = prev->offset + size;
> +}
> +
> +static void *generate_lfp_data_ptrs(struct drm_i915_private *i915,
> +				    const void *bdb)
> +{
> +	int i, size, table_size, block_size, offset;
> +	const void *t0, *t1, *block;
> +	struct bdb_lvds_lfp_data_ptrs *ptrs;
> +	void *ptrs_block;
> +
> +	block = find_raw_section(bdb, BDB_LVDS_LFP_DATA);
> +	if (!block)
> +		return NULL;
> +
> +	drm_dbg_kms(&i915->drm, "Generating LFP data table pointers\n");
> +
> +	block_size = get_blocksize(block);
> +
> +	size = block_size;
> +	t0 = find_fp_timing_terminator(block, size);
> +
> +	size -= t0 - block - 2;
> +	t1 = find_fp_timing_terminator(t0 + 2, size);

Need to NULL check t0 before using it.

I'll still keep trying to wrap my head around the below stuff.

> +
> +	if (!t0 || !t1)
> +		return NULL;
> +
> +	size = t1 - t0;
> +	if (size * 16 > block_size)
> +		return NULL;
> +
> +	ptrs_block = kzalloc(sizeof(*ptrs) + 3, GFP_KERNEL);
> +	if (!ptrs_block)
> +		return NULL;
> +
> +	*(u8 *)(ptrs_block + 0) = BDB_LVDS_LFP_DATA_PTRS;
> +	*(u16 *)(ptrs_block + 1) = sizeof(*ptrs);
> +	ptrs = ptrs_block + 3;
> +
> +	table_size = sizeof(struct lvds_pnp_id);
> +	size = make_lfp_data_ptr(&ptrs->ptr[0].panel_pnp_id, table_size, size);
> +
> +	table_size = sizeof(struct lvds_dvo_timing);
> +	size = make_lfp_data_ptr(&ptrs->ptr[0].dvo_timing, table_size, size);
> +
> +	table_size = t0 - block + 2;
> +	size = make_lfp_data_ptr(&ptrs->ptr[0].fp_timing, table_size, size);
> +
> +	if (ptrs->ptr[0].fp_timing.table_size)
> +		ptrs->lvds_entries++;
> +	if (ptrs->ptr[0].dvo_timing.table_size)
> +		ptrs->lvds_entries++;
> +	if (ptrs->ptr[0].panel_pnp_id.table_size)
> +		ptrs->lvds_entries++;
> +
> +	if (size != 0 || ptrs->lvds_entries != 3) {
> +		kfree(ptrs);
> +		return NULL;
> +	}
> +
> +	size = t1 - t0;
> +	for (i = 1; i < 16; i++) {
> +		next_lfp_data_ptr(&ptrs->ptr[i].fp_timing, &ptrs->ptr[i-1].fp_timing, size);
> +		next_lfp_data_ptr(&ptrs->ptr[i].dvo_timing, &ptrs->ptr[i-1].dvo_timing, size);
> +		next_lfp_data_ptr(&ptrs->ptr[i].panel_pnp_id, &ptrs->ptr[i-1].panel_pnp_id, size);
> +	}
> +
> +	size = t1 - t0;
> +	table_size = sizeof(struct lvds_lfp_panel_name);
> +
> +	if (16 * (size + table_size) <= block_size) {
> +		ptrs->panel_name.table_size = table_size;
> +		ptrs->panel_name.offset = size * 16;
> +	}
> +
> +	offset = block - bdb;
> +
> +	for (i = 0; i < 16; i++) {
> +		ptrs->ptr[i].fp_timing.offset += offset;
> +		ptrs->ptr[i].dvo_timing.offset += offset;
> +		ptrs->ptr[i].panel_pnp_id.offset += offset;
> +	}
> +
> +	if (ptrs->panel_name.table_size)
> +		ptrs->panel_name.offset += offset;
> +
> +	return ptrs_block;
> +}
> +
>  static void
>  init_bdb_block(struct drm_i915_private *i915,
>  	       const void *bdb, enum bdb_block_id section_id,
>  	       size_t min_size)
>  {
>  	struct bdb_block_entry *entry;
> +	void *temp_block = NULL;
>  	const void *block;
>  	size_t block_size;
>  
>  	block = find_raw_section(bdb, section_id);
> +
> +	/* Modern VBTs lack the LFP data table pointers block, make one up */
> +	if (!block && section_id == BDB_LVDS_LFP_DATA_PTRS) {
> +		temp_block = generate_lfp_data_ptrs(i915, bdb);
> +		if (temp_block)
> +			block = temp_block + 3;
> +	}
>  	if (!block)
>  		return;
>  
> @@ -330,12 +460,16 @@ init_bdb_block(struct drm_i915_private *i915,
>  
>  	entry = kzalloc(struct_size(entry, data, max(min_size, block_size) + 3),
>  			GFP_KERNEL);
> -	if (!entry)
> +	if (!entry) {
> +		kfree(temp_block);
>  		return;
> +	}
>  
>  	entry->section_id = section_id;
>  	memcpy(entry->data, block - 3, block_size + 3);
>  
> +	kfree(temp_block);
> +
>  	drm_dbg_kms(&i915->drm, "Found BDB block %d (size %zu, min size %zu)\n",
>  		    section_id, block_size, min_size);

-- 
Jani Nikula, Intel Open Source Graphics Center