linux-kernel - Re: [PATCH] tty: samsung_tty: 32-bit access for TX/RX hold registers

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Date:   Wed, 1 Apr 2020 11:19:52 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Hyunki Koo <hyunki00.koo@...sung.com>, hyunki00.koo@...il.com,
        Kukjin Kim <kgene@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: samsung_tty: 32-bit access for TX/RX hold registers

On Wed, Apr 01, 2020 at 10:55:48AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Apr 01, 2020 at 05:27:20PM +0900, Hyunki Koo wrote:
> > -	if (np)
> > +	if (np) {
> >  		of_property_read_u32(np,
> >  			"samsung,uart-fifosize", &ourport->port.fifosize);
> >  
> > +		if (of_property_read_u32(np, "reg-io-width", &prop) == 0) {
> > +			switch (prop) {
> > +			case 1:
> > +				ourport->port.iotype = UPIO_MEM;
> > +				break;
> > +			case 4:
> > +				ourport->port.iotype = UPIO_MEM32;
> > +				break;
> > +			default:
> > +				dev_warn(&pdev->dev, "unsupported reg-io-width (%d)\n",
> > +						prop);
> > +				ret = -EINVAL;
> > +				break;
> > +			}
> > +		}
> > +	}
> > +
> 
> Does this mean that reg-io-width is now a required property for all
> samsung uarts?  Does this break older dts files?  Or should you
> fall-back to the previous operation if the attribute is not there?

Yes, it looks like silently breaking all boards.  Since
of_property_read_u32() will return errno, the warning message won't be
printed and all register reads will fail (return 0).

This looks like not tested on real HW.

Best regards,
Krzysztof