[U-Boot] [PATCH v3 13/18] lcd: Add support for flushing LCD fb from dcache after update

[Simon Glass]

Hi Eric,

On Wed, Oct 17, 2012 at 5:41 PM, Eric Nelson
<eric.nelson at boundarydevices.com> wrote:
> Hi Simon,
>
>
> On 10/17/2012 03:07 PM, Simon Glass wrote:
>>
>> Hi Eric,
>>
>> On Wed, Oct 17, 2012 at 8:34 AM, Eric Nelson
>> <eric.nelson at boundarydevices.com>  wrote:
>>>
>>> On 10/17/2012 03:38 AM, Lukasz Majewski wrote:
>>>>
>>>>
>>>> <snip>
>>>>
>>>>
>>>>> Certainly we could make the flushing more fine grained. My reasons for
>>>>> not (so far) are:
>>>>>
>>>>> 1. It is simpler to flush everything (no need to figure out what part
>>>>> of display has changed)
>>>>> 2. The performance difference is likely to be small since flushing an
>>>>> already-flushed range should be fast.
>>>>
>>>>
>>>>
>>>>    From the sake of "SW engineering" I would opt for fine grained
>>>> flushing. But if it turns out, that it costs too much, we can flush
>>>> everything.
>>>>
>>>
>>> Is anybody else in a position to get some numbers about how/if
>>> performance is better when flushing at the more granular level?
>>>
>>> Before deciding it wasn't worth the code, I implemented granular
>>> flushing and didn't see any noticeable degradation when just
>>> flushing at the end of all public functions as in this patch.
>>>
>>>          http://lists.denx.de/pipermail/u-boot/2012-September/134979.html
>>>
>>> It seems that performance is the only reason for fine-grained
>>> cache flush operations
>>
>>
>> Also we might be talking about different things. I have taken the
>> approach of flushing the whole display, but only after some display
>> functions. We could flush only what has changed, which is what I was
>> referring to as 'fine-grained'. You may have meant the idea of
>> flushing after every function that touches the display, or a
>> 'fine-grained' approach of only flushing after some functions.
>>
>
> You're right. That's what I get for chiming in quickly before
> attending a customer meeting: I jump to conclusions.
>
> I thought 'finer-grained' referred to the way Anatolij originally
> did things:
>
> http://git.denx.de/?p=u-boot.git;a=commit;h=bfd4be803bbb7d122c2e3aaf6eaf987efa8d69da
>
> I tried to follow that lead, but it degenerated into a horrible
> mess of alignment checking.
>
>
>> My testing shows that flushing is pretty fast, but I was reluctant to
>> flush after every putc() as it seemed egregiously inefficient.
>>
>
> I need to spend some time with the patch to figure out how you
> get around cache issues for keystroke echo.

Well my less-than-lovely approach was to use puts() for all character
echo. That has a flush.

Regards,
Simon

>
> Regards,
>
>
> Eric