[U-Boot] [linux-sunxi] [u-boot 2/2] sun5i: bump DEBE priority (useful on a10s only)

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 20-01-15 09:16, Siarhei Siamashka wrote:
> On Mon, 19 Jan 2015 06:29:47 +0200
> Siarhei Siamashka <siarhei.siamashka@gmail.com> wrote:
>
>> On Sun, 04 Jan 2015 20:49:38 +0100
>> Hans de Goede <hdegoede@redhat.com> wrote:
>>
>>> Hi,
>>>
>>> On 04-01-15 20:19, Michal Suchanek wrote:
>>>>     Setting magic 'reserved' hpcr bit on sun5i DEBE seems required for
>>>>     smooth HDMI scanout of large frambuffer (eg. 1080p).
>>>>
>>>>     This fix comes at the cost of some overall memory bandwidth so it
>>>>     might be appropriate to detect a10s and only apply there (and not a13).
>>>
>>> Hmm, Sairhei is the expert on this, adding him to the Cc. Sairhei, what
>>> do you think of the proposed change ?
>>
>> I don't have A10s hardware, so have no idea and can't test anything
>> myself.
>>
>> It would be great to have a better description of what exactly is
>> happening before the patch. And precisely how the patch is helping.
>> A description of the test setup and benchmark numbers would be
>> appreciated. And it would be perfect if somebody else could reproduce
>> the test and confirm the results.
>>
>> I may try to check A20 with the bus width artificially reduced
>> to 16 bits (not a totally unrealistic configuration, since
>> A20-OLinuXino-LIME board exists). If sun5i and sun7i are similar
>> enough, then the magic reserved bit may have some effect there too.
>> But that's a different hardware either way.
>
> Done these tests with A20. Ironically, now the tables have turned and
> A10 seems to be doing a better job than A20 at low DRAM clock speeds
> (~408MHz) and 16-bit bus width when dealing with full-hd monitors.
>
> Just like Michal observed on A10s, setting 0x5031 as DEFE host port
> config makes things much worse on A20. Overall, the test results look
> in the following way on A20 with 16-bit DRAM clocked at 408MHz (yes,
> none of the real boards uses such a slow DRAM setup) while running
> lima-memtester and driving 1920x1080-32 at 60Hz monitor:
>
> 0x1035 - The screen regularly blanks, but comes back again instantly.
> 0x1037 - The screen regularly blanks, but comes back again instantly.
> 0x5031 - Severe screen shaking.
>
> Unlike A10, there does not seem to be any difference between using DEBE
> or DEFE for framebuffer scanout on A20, so using DEBE has the same
> effect as listed above. Setting the magic 'reserved' hpcr bit 1
> (0x1037 value) does not seem to have any effect on sun7i. It is
> great that it is apparently helping on sun5i/A10s though.

Thanks for running these tests, this makes me more confident that I
only need to enable DEFE in u-boot on A10, and can directly use
DEBE on the others.

Regards,

Hans