linux-kernel - Re: [PATCH 2.6.19-rc1 V9] drivers: add LCD support

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Date:	Sun, 8 Oct 2006 18:24:38 +0000
From:	Pavel Machek <pavel@....cz>
To:	Miguel Ojeda Sandonis <maxextreme@...il.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.19-rc1 V9] drivers: add LCD support

Hi!

> Andrew, I think this can be the final review.
> Updated to 2.6.19-rc1. Please apply.

No, I'm sorry. And I have to apologize for being blind.

I was going to say 'this is very important, because cellphones *do*
have secondary displays, and we want to use them'. And yes it is
important, but you got the interface wrong.


> +		The cfag12864b LCD driver defines two ways to communicate
> +		with the lcd.
> +
> +		1. Use seek and write syscalls. Bytes written appear on
> +		   the screen without any formatting on the position pointed
> +		   by the file offset.
> +
> +		   It is hardware dependent. It should be use to modify
> +		   specific display's pixels to achieve higher refreshing
> +		   rates.
> +
> +		2. Use ioctl syscall. The magic number is 0xFF.
> +		   There are four ioctls:
> +
> +		   2.0. off	_IO(0xFF,0)
> +
> +			Power off display.
> +
> +			It doesn't clear the display.
> +			It doesn't stop the controllers.
> +
> +		   2.1. on	_IO(0xFF,1)
> +
> +			Power on display.
> +
> +		   2.2. clear	_IO(0xFF,2)
> +
> +			Clear the display.
> +
> +		   2.3. format	_IOW(0xFF,3,void *)
> +
> +			Read the given buffer, transform it to the hardware
> +			dependent format and show it on the screen.
> +
> +			The argument must point to a userspace buffer of
> +			size 128*64 bytes (the display's size).
> +
> +			Each buffer's byte (unsigned) represent a pixel:
> +				0  = pixel will turn off
> +				>0 = pixel will turn on
> +
> +		For more information and examples, see
> +		Documentation/auxdisplay/cfag12864b

So you have 128x64 pixels b/w display, and invented completely new
interface to control it.

Fortunately we already have good interface for the display... It is
called fbcon, and is more flexible than 128x64 b/w... but can do
128x64 b/w just fine.

Please use it. It is way more flexible, and it is right thing to do.

						Pavel
-- 
Thanks for all the (sleeping) penguins.
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