linux-kernel - Re: [PATCH v3 2/4] Watchdog: sp5100_tco: Refactor MMIO base address initialization

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Date:   Tue, 25 Jan 2022 17:38:57 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     Terry Bowman <Terry.Bowman@....com>
Cc:     linux@...ck-us.net, linux-watchdog@...r.kernel.org,
        linux-i2c@...r.kernel.org, wsa@...nel.org,
        andy.shevchenko@...il.com, rafael.j.wysocki@...el.com,
        linux-kernel@...r.kernel.org, wim@...ux-watchdog.org,
        rrichter@....com, thomas.lendacky@....com,
        Nehal-bakulchandra.Shah@....com, Basavaraj.Natikar@....com,
        Shyam-sundar.S-k@....com, Mario.Limonciello@....com
Subject: Re: [PATCH v3 2/4] Watchdog: sp5100_tco: Refactor MMIO base address
 initialization

On Tue, 25 Jan 2022 09:18:59 -0600, Terry Bowman wrote:
> On 1/25/22 7:45 AM, Jean Delvare wrote:
> > On Tue, 18 Jan 2022 14:22:32 -0600, Terry Bowman wrote:  
> >> +static int __sp5100_tco_prepare_base(struct sp5100_tco *tco,
> >> +				     u32 mmio_addr,
> >> +				     const char *dev_name)
> >> +{
> >> +	struct device *dev = tco->wdd.parent;
> >> +	int ret = 0;
> >> +
> >> +	if (!mmio_addr)
> >> +		return -ENOMEM;  
> > 
> > Can this actually happen? If it does, is -ENOMEM really the best error
> > value?
> 
> This can happen if mmio_addr is not assigned in sp5100_tco_setupdevice_mmio() 
> before calling sp5100_tco_prepare_base() and __sp5100_tco_prepare_base().

Ah yes, I can see it now.

> I can move the NULL check out of __sp5100_tco_prepare_base() and into
> sp5100_tco_prepare_base() before calling __sp5100_tco_prepare_base().
> As you describe below.
> 
> The ENOMEM return value should be interpreted as the mmio_addr is not 
> available. EBUSY does not describe the failure correctly because EBUSY 
> implies the resource is present and normally available but not available 
> at this time. Do you have a return value preference ?

Well, if one mmio_addr isn't set, you shouldn't call
__sp5100_tco_prepare_base() for it so there's no error to return. If
neither mmio_addr is set then the hardware is simply not configured to
be used, so that would be a -NODEV returned by
sp5100_tco_prepare_base() I suppose?

BTW...
 
> >> (...)
> >> +	if (ret)
> >> +		dev_err(dev, "Failed to reserve-map MMIO (%X) and alternate MMIO (%X) regions. ret=%X",
> >> +			mmio_addr, alt_mmio_addr, ret);  

... I think that should be a "or" rather than "and", and singular
"region", in this error message? I mean, the plan was never to
reserve-map both of them, if I understand correctly.

-- 
Jean Delvare
SUSE L3 Support