linux-kernel - Re: [PATCH v2 28/32] auxdisplay: hd44780: Remove clear

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Message-ID: <20200922052227.GA16386@1wt.eu>
Date:   Tue, 22 Sep 2020 07:22:27 +0200
From:   Willy Tarreau <w@....eu>
To:     poeschel@...onage.de
Cc:     Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 28/32] auxdisplay: hd44780: Remove clear_fast

Hi Lars,

On Mon, Sep 21, 2020 at 04:46:40PM +0200, poeschel@...onage.de wrote:
> From: Lars Poeschel <poeschel@...onage.de>
> 
> We remove the hd44780_clear_fast (display) clear implementation. charlcd
> will fall back to use hd44780_common_clear_display then, which is much
> much faster.

I might have got confused, but it looks to me like patches 27 and 28
basically undo patch 26: in 26 you moved code to hd44780 and wrote a
fallback, just to later delete that code.

I seem to remember that the reason for the clear_fast() implementation
is that the default clear_display() is quite slow for small displays,
compared to what can be achieved by just filling the display with spaces
(in the order of tens of milliseconds vs hundreds of microseconds). But
I could be mistaken given how old this is, so please take my comment
with a grain of salt.

Willy