Claude review: drm/exynos: fbdev: Calculate buffer geometry with format helpers

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Status: Good, one minor note**

This replaces the hand-rolled geometry calculation with proper DRM format helpers. The v3 error checks are thorough:

```c
fourcc = drm_mode_legacy_fb_format(sizes->surface_bpp, sizes->surface_depth);
if (fourcc == DRM_FORMAT_INVALID)
    return -EINVAL;
format = drm_get_format_info(dev, fourcc, DRM_FORMAT_MOD_LINEAR);
if (!format)
    return -EINVAL;
pitch = drm_format_info_min_pitch(format, 0, sizes->surface_width);
if (!pitch)
    return -EINVAL;
if (check_mul_overflow(pitch, sizes->surface_height, &size))
    return -EINVAL;
size = ALIGN(size, PAGE_SIZE);
if (size < PAGE_SIZE)
    return -EINVAL;
```

**Minor note on types:** `drm_format_info_min_pitch()` returns `uint64_t` but `pitch` is declared as `u32`. For fbdev surface sizes this is never a practical issue, and the resulting pitch is consumed by `mode_cmd.pitches[0]` (also `u32`) and `drm_client_buffer_create(..., u32 pitch)`, so `u32` is the right type for the interface contract. The `!pitch` check catches the degenerate case where the return was 0. If the pitch somehow exceeded 32 bits (theoretically impossible for reasonable fbdev sizes), it would silently truncate, but this matches the existing API constraints.

The switch to `obj->size` for `screen_size` and `fix.smem_len` is correct — it reflects the actual allocated size (which may be larger than the requested size after GEM allocation alignment):
```c
+	info->screen_size = obj->size;
+	info->fix.smem_len = obj->size;
```

No blocking concerns.

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Generated by Claude Code Patch Reviewer