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SubjectRe: staging: panel: suggestions needed
Hi Sudip,

[ CCing Mariusz who's currently cleaning up the driver ]

On Tue, Dec 02, 2014 at 01:32:14PM +0530, Sudip Mukherjee wrote:
> Hi,
> I have been looking at your panel driver, and am attaching a 20x4 alphanueric
> lcd to it. Will start testing it in a few days as and when I get time. Looks
> like, it is receiving mostly checkpatch and sparse cleanups.

yes mostly.

> Just wanted your opinion on few things I was thinking:
> 1) Number of lines you have fixed to 2 and 40 char per line. since I am
> going to connect 20x4 , i need to remember that after displaying 20
> character in 1st line, next char will come to 3rd line. instead why
> don't we make the option of number of line to 4 ?

Feel free to do so. I never had the luck to own a 4-line LCD so this
was never even planned. And yes, I remember something about 4-line LCDs
using tricks such as 2x40 addressing being split into 4x20.

> 2) The lcd commands you are writing to the lcd in an escape sequence
> while writing to the lcd. Instead of that why don't we use ioctl for
> lcd commands, and writing to the device will involve only sending data
> to lcd ?

Because you cannot send that from a script. It's just as if you had to use
an ioctl to clear your terminal, inverse its video or to move its cursor,
it would not be very convenient.

> 3) You have given fixed minor number in your code. Any problem if we
> make it dynamic ?

No objection, but I think we should keep a config option to bind to the
old minor. The rationale behind this is that this driver is mostly used
in embedded systems with a fixed /dev.

> 4) For now I am only attaching a LCD, but I also want to attach a
> keypad to it. Can you please let me know about the schematic of the
> keypad connection? I can find out from the code, but I have not yet
> seen the keypad code.

It used to be documented as an ASCII-art diagram but I can't find that
anymore :-/ IIRC you had to wire buttons between some of the outputs and
some of the inputs. From what I remember, it was possible to detect that
an input is :
- tied to ground
- tied to a data line
- tied to a control line

I found this comment in the old source file :
"document 24 keys keyboard (3 rows of 8 cols, 32 diodes + 2 inputs)"

So maybe we only use data lines and not control lines.

And the keypad code periodically scans all outputs and notes inputs states.
The Nexcom profile works with the keypad, though I don't have the wiring
in mind. It uses 4 keys. It should be easy to find that from the code

Hmmm I found an old description of 2001 (kernel 2.2.18) from the one of the
first circuit I made (with a serial lcd). It involved the smartcard detector
(now removed) and 6 keys :

strobe -> lcd.strobe
d0 -> lcd.serial.din (serial) + lcd.parallel.d0 + keypad.k0
d1 -> d7 => lcd.parallel.d1-d7 + keypad.k1-k7
ack <- smartcard.dout
busy <-
pe <- (keypad common1 if more than 8 keys)
select <- keypad common0
autofeed -> lcd.serial.backlight /
error <- smartcard.detector
init ->
select_in ->

And here's the module load command I used to run :
insmod /tmp/panel-0.8.0.o parport=0 lcd_enabled=2 keypad_enabled=1 lcd_width=16 lcd_hwidth=16 lcd_height=2

Hoping this helps,

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