linux-kernel - Re: [PATCH v3 2/3] ata: ahci

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Date:	Thu, 9 Jan 2014 11:05:20 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Roger Quadros <rogerq@...com>
Cc:	Kishon Vijay Abraham I <kishon@...com>, tj@...nel.org,
	sergei.shtylyov@...entembedded.com, b.zolnierkie@...sung.com,
	hdegoede@...hat.com, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Balaji T K <balajitk@...com>
Subject: Re: [PATCH v3 2/3] ata: ahci_platform: Manage SATA PHY

On Thursday 09 January 2014, Roger Quadros wrote:
> >> if (!IS_ERR(hpriv->phy)) {
> >>         rc = phy_init(hpriv->phy);
> >>         if (rc)
> >>                 goto disable_unprepare_clk;
> >>
> >>         rc = phy_power_on(hpriv->phy);
> >>         if (rc) {
> >>                 phy_exit(hpriv->phy);
> >>                 goto disable_unprepare_clk;
> >>         }
> >> }
> > 
> > As I said, I'd prefer to set hpriv->phy to NULL in case of -ENODEV,
> > but functionally it seems right (with the fixup from your other mail).
> > 
> 
> Why do you prefer setting hpriv->phy to NULL instead of using IS_ERR() check
> before hpriv->phy is used?
> The latter seems to be the norm at least among clock framework users.

Two reasons:

1. It feels more natural to read "if (clk)" in driver code as a check for
   "a clock exists" than "if (!IS_ERR(clk))".
2. It clarifies that this code path is only there to check for the
   clk-not-present case, not for other errors.

Obviously the first check after clk_get needs to be IS_ERR() because that
is the documented interface, but then you should decide on the action
based on the specific error.

	Arnd
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