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

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Message-ID: <20200402094808.GA21903@kozik-lap>
Date:   Thu, 2 Apr 2020 11:48:08 +0200
From:   'Krzysztof Kozlowski' <krzk@...nel.org>
To:     Hyunki Koo <hyunki00.koo@...sung.com>
Cc:     'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>,
        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 Thu, Apr 02, 2020 at 06:44:58PM +0900, Hyunki Koo wrote:
> 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;
> +		}

Thanks. Also, please test your patch on available Exynos boards, e.g.
Odroid XU4 or HC1.

Best regards,
Krzysztof