Re: How to allocate hugepage in kernel module?

[aurum spark]

Hi J.Hwan Kim,

Before we talk about APIs let's understand few things about requirement
1. How much contiguous memory do you require for you module ?
2. Should it be DMAble ?
3. Are you going to use that as shared memory with any other card or processor ?

So there are certain API which can provide you huge chunk of contiguous memory.
1. One of them as you are using is get_free_pages(). Try suggestions
by others to get rid of error.
2. Another thing you can use is dma_alloc_coherent(). But there is
limit on this and you should consider that other modules will also
required DMAble memory.
3. Depending on the kernel version you are using you can do
bootmem_reserve() API during initialization code of kernel and you can
keep this memory reserved for your module. Pass that as platform data.
4. You can try passing say mem=768M parameter through kernel
commandline(assuming you have 1G of memory). That will force kernel to
use 768M and you can use rest of the 256M memory by doing ioremap in
your module.

Regards,
~/Aurum

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Writing I2C chip driver in combination with other structure

[aurum spark]

Hi All,

I have written and seen lot of code of i2c drivers for input subsystem
devices and much familiar with that. Now I have started writing driver
for one chip that is not exactly type of input device. So, little bit
confused about how should be the driver architecture so that it will
be a clean code yet simple.  Following text and diagram explains short
functional description of chip.


Chip Interface :-
==


==   ===
| ||   I2C |
| | - I2C ---  |  Device|
|ARM  | - Bus --  |  With rw|  Input Connect
| ||   regs   |
| | ---| |
== INTR   ===

So above picture depicts how chip is interfaced to ARM CPU. This chip
has some registers which are rw and can be used to read certain
information from chip or to program it. This chip is capable of giving
intterupt to CPU. This chip has one input which it like some cable
connection. It detects when this cable is connected and raises the
interrupt.

Functionality Expected in Driver:-
===

1. Driver should communicate with chip over I2C.
2. Driver should report event to user space upon receiving interrupt
from I2C device.
3. Driver should be capable of programming I2C chip @ the time of
initialization as well should be capable of changing registers as and
when Linux User Space application wants to.

What I have thought of:-
==

#1 definitely makes this as i2c client driver(chip driver)

#2 Here I have few options

 a) Shall I use input subsystem mechanism to report interrupt as an
event to user space ? In this case it's combination of I2C + input
subsystem. Then application can read something over i2c and decide
next flow,

 OR

 b) Shall I use some sysfs based interface on which application can do
select sys call and can receive event ? for this nothing extra
required.

#3 Since approach in #2 is not fixed here also there are multiple options
a) This  can be written as I2C client + char driver so that it can
have ioctls to send commands to i2c chip based on applications demand.
b) We can provide sysfs interface to user space to send commands to
i2c device as and when required at runtime.


As per my thoughts I am not sure shall I make this as input device
just to report one event upon getting interrupt from device. Also will
it be ok to have this as char driver in combination with i2c chip
driver ?

Please guide me and take me to correct source or documentation or to
source code of some driver for this kind of device. Does i2c support
ops like fbops ?


Regards,
 ~/Aurum

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