linux-kernel - Re: [PATCH 1/1] linux/io.h: Add cleanup defination for iounmap() and memunmap()

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Message-ID: <ZqumhgZ5heh0OYuA@lizhi-Precision-Tower-5810>
Date: Thu, 1 Aug 2024 11:15:18 -0400
From: Frank Li <Frank.li@....com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Jason Gunthorpe <jgg@...pe.ca>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	open list <linux-kernel@...r.kernel.org>, imx@...ts.linux.dev
Subject: Re: [PATCH 1/1] linux/io.h: Add cleanup defination for iounmap() and
 memunmap()

On Thu, Aug 01, 2024 at 09:27:40AM +0200, Arnd Bergmann wrote:
> On Thu, Aug 1, 2024, at 01:31, Frank Li wrote:
> > Add DEFINE_FREE for iounmap() and memunmap() to support scope based
> > cleanup.
> >
> > Signed-off-by: Frank Li <Frank.Li@....com>
> > ---
> >  include/linux/io.h | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/include/linux/io.h b/include/linux/io.h
> > index 59ec5eea696c4..7695d7973c8ff 100644
> > --- a/include/linux/io.h
> > +++ b/include/linux/io.h
> > @@ -163,6 +163,9 @@ enum {
> >  void *memremap(resource_size_t offset, size_t size, unsigned long flags);
> >  void memunmap(void *addr);
> >
> > +DEFINE_FREE(iounmap, void __iomem *, if (!IS_ERR_OR_NULL(_T)) iounmap(_T))
> > +DEFINE_FREE(memunmap, void *, if (!IS_ERR_OR_NULL(_T)) memunmap(_T))
>
> I don't like the use of IS_ERR_OR_NULL(), which tends
> to indicate a problem in the interface design.

Just !(_T) ? I just refer kfree()'s implementation.

>
> In which cases do you expect to need scope based cleanup
> on an error pointer here? The only interfaces I see that
> returns an __iomem error pointer are the devm_* ones, but
> those have their own cleanup method.


devm_* can help much especial in probe() function. but scope base cleanup
also useful.

Give a existed example:

drivers/clocksource/timer-fsl-ftm.c

static int __init ftm_timer_init(struct device_node *np) {
	...
	priv->clksrc_base = of_iomap(np, 1);
        if (!priv->clksrc_base) {
                pr_err("ftm: unable to map source timer registers\n");
                goto err_clksrc;
        }
	...

err_clksrc:
        iounmap(priv->clkevt_base);
}

If use scoped base cleanup it will be simple.
ftm_timer_init()
{
	base __free(ioumap) =  of_iomap(np, 1);

	...
	priv->clksrc_base = no_free_ptr(base);
	return 0;
}

drivers/clocksource/arm_arch_timer.c
Some example need map and unmap in function such as:
arch_timer_mem_frame_get_cntfrq()
{
	base = ioremap(frame->cntbase, frame->size);
	...
	iounmap(base);
}

of course this example is too simple. If there are many error branch
between ioremap() and iounmap(), scoped based clean up make code simple.

Frank

>
>     Arnd