[Intel-gfx] [PATCH 1/3] drm: Add new DRM_IOCTL_MODE_GETPLANE2

[Daniel Stone]

Hi,

On 12 January 2017 at 17:45, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
> On Thu, Jan 12, 2017 at 05:04:46PM +0000, Daniel Stone wrote:
>> Implicit is clever but horrible. AFAICT, the only way to do it
>> properly would be to have a nested forwards loop walk when you first
>> hit a modifier, searching for further occurrences of that modifier to
>> collect the complete set of formats that modifier applies to.
>
> Not sure for what that is the "only way". In fact I can't right now
> think of any operation that would require an extra loop necessarily.
> For some things you might just want to look for a specific
> format+modifier combo, for that it doesn't matter how many blocks there
> are.

Right, that just needs a local variable to act as a counter.

> And if you want to transform the reply into some less convoluted
> form, well then you'd just need some modifier+dynamic format list thing,
> or if you want to keep to bitmasks you'd either need a bitmask that can
> grow when running out of bits or just make it big enough to handle a
> sufficiently large worst case number of bits.
>
> Dunno, maybe I just lack imagination. Then again, I'm not even sure if
> we're talking about userspace of kernel code here, which might explain
> my general confusion :)

I'm talking about userspace, where I want to have:
struct drm_plane {
    struct {
        uint32_t format;
        uint64_t modifiers[];
    } formats[];
}

Rather than keeping the original format around and doing the lookup every time.

Cheers,
Daniel