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Date:   Wed, 22 Apr 2020 23:07:14 +0200
From:   "Erhard F." <erhard_f@mailbox.org>
To:     Wolfram Sang <wsa@the-dreams.de>
Cc:     Aishwarya R <aishwaryarj100@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Richard Fontana <rfontana@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-i2c@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] i2c: powermac: Simplify reading the "reg" and
 "i2c-address" property
Message-ID: <20200422230709.19a81ef9@supah>
In-Reply-To: <20200421093712.GA1241@ninjato>
References: <20200408100354.17782-1-aishwaryarj100@gmail.com>
        <20200415131916.23555-1-aishwaryarj100@gmail.com>
        <20200421093712.GA1241@ninjato>
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On Tue, 21 Apr 2020 11:37:13 +0200
Wolfram Sang <wsa@the-dreams.de> wrote:

> On Wed, Apr 15, 2020 at 06:49:14PM +0530, Aishwarya R wrote:
> > >> Use of_property_read_u32 to read the "reg" and "i2c-address" property
> > >> instead of using of_get_property to check the return values.
> > >>
> > >> Signed-off-by: Aishwarya R <aishwaryarj100@gmail.com>  
> >   
> > > This is quite a fragile driver. Have you tested it on HW?  
> > 
> > This change is not tested with the Hardware.
> > But of_property_read_u32 is better here than generic of_get_property.
> > This make sure that value read properly independent of system endianess.  
> 
> This driver is only used on PPC_BE. And it is *very* fragile. The gain
> is not enough for me to accept it without testing. Maybe Erhard (CCed)
> is interested. If not, you may find someone on the ppc lists.
> 

I applied the patch on top of kernel 5.6.6 and tested it on a PowerMac G4 3,6 DP and a PowerMac G5 11,2. Both machines run without anything suspicious going on. dmesg | grep i2c looks the same with patch and without patch.

Tested-by: Erhard Furtner <erhard_f@mailbox.org>