linux-kernel - Re: [PATCH] serial: amba-pl011: do not request memory region twice

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Message-ID: <YaEGvkBl8YT33YAR@shell.armlinux.org.uk>
Date:   Fri, 26 Nov 2021 16:09:34 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        p.rosenberger@...bus.com, lukas@...ner.de,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: amba-pl011: do not request memory region twice

On Fri, Nov 26, 2021 at 03:39:25PM +0100, Lino Sanfilippo wrote:
> The driver attempts to request and release the IO memory region for a uart
> port twice:
> 
> First during the probe() function devm_ioremap_resource() is used to
> allocate and map the ports memory.
> Then a combo of pl011_config_port() and pl011_release_port() is used to
> request/release the same memory area. These functions are called by the
> serial core as soon as the uart is registered/unregistered.
> 
> However since the allocation request via devm_ioremap_resource() already
> succeeds, the attempt to claim the memory again via pl011_config_port()
> fails. This failure remains unnoticed, since the concerning return value is
> not evaluated.
> Later at module unload also the attempt to release the unclaimed memory
> in pl011_release_port() fails. This time the failure results in a “Trying
> to free nonexistent resource" warning printed by the serial core.
> 
> Fix these issues by removing the callbacks that implement the redundant
> memory allocation/release.

I think you will also need the verify_port method to also deny changing
port->mapbase.

-- 
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