Best practice to lock a read/write to a HW register

Hi all,
can someone please show me which is the best practice to lock a read/write to a hardware register.
In other words if, in a driver, I want to modify a bit in a HW register, I have to read the register, set/reset the relevant bit and write back the reg.
But what can I do to be sure that no other code modifies the register between my read and write?
Is spin_lock() suitable for this purpose?
Thanks
Best regards
Luca

If IRQ handlers can touch this register, then I think you'll have to disable interrupts as well (spin_lock_irq*() ?).

HTH,
-mandep

Hi Luca

The locking mechanism to be used depends on what your piece of code does and where your code runs.
If your code runs in a interrupt context (inside an interrupt handler), you should use a spinlock (with irq save and restore). Else you can use mutex or a semaphore.

In either cases, you don't lock the hardware register but create a lock descriptor and lock the same. So you need to implement locking at every place the register is accessed.

Please refer http://lwn.net/Kernel/LDD3/ on how to use locks.

Regards,
Binoy Jayan

________________________________________
From: [email protected] [kernelnewbies-bounces at kernelnewbies.org] on behalf of Luca Ellero [lroluk at gmail.com]
Sent: Thursday, November 14, 2013 4:02 PM
To: kernelnewbies at kernelnewbies.org
Subject: Best practice to lock a read/write to a HW register

Hi all,
can someone please show me which is the best practice to lock a read/write to a hardware register.
In other words if, in a driver, I want to modify a bit in a HW register, I have to read the register, set/reset the relevant bit and write back the reg.
But what can I do to be sure that no other code modifies the register between my read and write?
Is spin_lock() suitable for this purpose?
Thanks
Best regards
Luca

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Hi!

On Don, 2013-11-14 at 11:32 +0100, Luca Ellero wrote:
[...]

If the read-modify-write (read: the critical section) run-time is short, a spin-lock is the usual means. If it is needed from IRQ-context - see also other mails - you must use the *_irq() variant.

Bernd

Bernd Petrovitsch                  Email : bernd at petrovitsch.priv.at
                     LUGA : http://www.luga.at

Ideally, it depends on the platform you are working. You need to discuss with them for the correct approach. For Qualcomm they have some hardware caled as RPU(Register protection unit). They have systems calls exposed for using them. You can associtate it to the register you want protection. I dont know if there is any way you could do it in Linux itself?

Regards,
Sandeep

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Thanks to all,
your suggestions are very appreciated
Best regards
Luca