multiple i2c_open() calls for same I2C port/address returns valid handles - should be single valid handle for each I2C Port/Address

[PSkeberdis]

Expecting that the first i2c_open for s specific port/address would provide a valid handle, but that a second i2c_open for the same port/address without a close would not provide a valid handle.

First instance of program run well, then second instance stomps the first instance as it also receives a valid handle.

Am testing on Pi4B+ running Ubuntu 21.04:
Distributor ID: Ubuntu
Description: Ubuntu 21.04
Release: 21.04
Codename: hirsute

Code snippet from lcd_i2c.py:
...
import lgpio
import time
from RPLCD.i2c import CharLCD

from datetime import datetime

address = 0x27

cols = 20
rows = 4

lcd = CharLCD(i2c_expander='PCF8574', address=address, port=1,
cols=cols, rows=rows,
charmap='A02', # A00, A02 or ST0B
backlight_enabled=True)
...

Fix would be to only issue a valid handle for I2C Port/address if a current handle for the same I2C Port/Address did not exist.

[joan2937]

That is by design. If the underlying operating system is happy to have the same device opened multiple times then so is lg.

[PSkeberdis]

I don’t agree with your design philosophy in that regard. The device driver is part of the OS and should be responsible for deconflicting device access. Here’s a reference for Linux device drivers from https://www.linuxjournal.com/article/2476: Do I Really Need to Write a Driver? There are several reasons for writing our own device driver: * To solve concurrency problems when two or more processes try to access a device at the same time. * To use hardware interrupts: as the kernel runs in protected mode, the user cannot manage interrupts directly from a program. * To handle other unusual applications, such as managing a virtual device (a RAM disk or a device simulator). * To obtain satisfaction as a programmer: writing a driver increases personal motivation as well as control over the computer. * To learn about the internal parts of the system. From: joan2937 ***@***.***> Sent: Thursday, August 05, 2021 3:30 AM To: joan2937/lg ***@***.***> Cc: PSkeberdis ***@***.***>; Author ***@***.***> Subject: Re: [joan2937/lg] multiple i2c_open() calls for same I2C port/address returns valid handles - should be single valid handle for each I2C Port/Address (#10) That is by design. If the underlying operating system is happy to have the same device opened multiple times then so is lg. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#10 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AUUJEBRQTEZ3ZEHP5TCT3FTT3I4XDANCNFSM5BSTWIWA> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&utm_campaign=notification-email> .