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

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Date:   Thu, 2 Apr 2020 18:44:58 +0900
From:   "Hyunki Koo" <hyunki00.koo@...sung.com>
To:     "'Krzysztof Kozlowski'" <krzk@...nel.org>,
        "'Greg Kroah-Hartman'" <gregkh@...uxfoundation.org>
Cc:     <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 6:20:20PM +0900, Krzysztof Kozlowski
wrote:
> 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

[Hyunki Koo] 
reg-io-width =4 is required for Samsung uart
To do not break older dts files, I will set default value in else of of_property_read_u32 like below.
+		if (of_property_read_u32(np, "reg-io-width", &prop) == 0) {
+ ...
+		} else {
+			ourport->port.iotype = UPIO_MEM;
+		}