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Subject: Re: [RFC PATCH v2 2/6] i2c: allow DT nodes without 'compatible'
To:     Wolfram Sang <wsa@the-dreams.de>
Cc:     Luca Ceresoli <luca@lucaceresoli.net>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        linux-i2c@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        linux-i3c@lists.infradead.org,
        =?UTF-8?Q?Niklas_S=c3=b6derlund?= <niklas.soderlund@ragnatech.se>,
        Jacopo Mondi <jacopo@jmondi.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Vladimir Zapolskiy <vz@mleia.com>,
        linux-kernel@vger.kernel.org,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Rob Herring <robh@kernel.org>
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From:   Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Organization: Ideas on Board
Message-ID: <dd627250-7916-8ac6-9a3c-316e0d7843ae@ideasonboard.com>
Date:   Wed, 15 Apr 2020 09:38:03 +0100
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Hi Wolfram,

On 15/04/2020 09:16, Wolfram Sang wrote:
> 
>> Aha, is it easy enough to distinguish that difference in user-space so
>> that we can present a specific character to indicate this in i2cdetect?
>> Or is that not so easy?
> 
> I thought about it shortly but have not come up with a way of doing
> that. This is the code in i2cdetect:
> 
> 	/* Set slave address */
> 	if (ioctl(file, I2C_SLAVE, i+j) < 0) {
> 		if (errno == EBUSY) {
> 			printf("UU ");
> 			continue;
> 		} else {
> 			fprintf(stderr, "Error: Could not set "
> 				"address to 0x%02x: %s\n", i+j,
> 				strerror(errno));
> 			return -1;
> 		}
> 	}
> 
> So, if we chose to use another errno to indicate 'reserved' and update
> i2cdetect, all old versions of i2cdetect will have ugly error messages.
> And adding another IOCTL just for printing reserved addresses neither
> sounds great.

Indeed, a different errno would be about all we could do - and it would
seemingly leave old i2cdetects with complete failures, if it goes
through that non-EBUSY code path.

Ayeeeee :-S

--
Kieran