Re: [PATCH v2 1/1] serial: 8250_dw: Allow hardware flow control to be used

From: James Hogan <james.hogan@imgtec.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Heiko Stuebner <heiko@sntech.de>,
	Jason Uy <jason.uy@broadcom.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Noam Camus <noamc@ezchip.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Wang Hongcheng <annie.wang@amd.com>,
	<linux-serial@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	<bcm-kernel-feedback-list@broadcom.com>,
	Linux MIPS Mailing List <linux-mips@linux-mips.org>,
	David Daney <david.daney@cavium.com>,
	Russell King <linux@armlinux.org.uk>, <linux-clk@vger.kernel.org>,
	Viresh Kumar <viresh.kumar@st.com>
Subject: Re: [PATCH v2 1/1] serial: 8250_dw: Allow hardware flow control to be used
Date: Fri, 3 Mar 2017 23:23:05 +0000	[thread overview]
Message-ID: <20170303232305.GU996@jhogan-linux.le.imgtec.org> (raw)
In-Reply-To: <1488547866.20145.74.camel@linux.intel.com>

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On Fri, Mar 03, 2017 at 03:31:06PM +0200, Andy Shevchenko wrote:
> On Fri, 2017-03-03 at 00:21 +0000, James Hogan wrote:
> > The CONFIG_HAVE_CLK=n implementation of devm_clk_get() in particular
> > seems highly questionable to me, given that commit 93abe8e4b13a ("clk:
> > add non CONFIG_HAVE_CLK routines") which added it 5 years ago says:
> > 
> > > These calls will return error for platforms that don't select
> > > HAVE_CLK
> > 
> > And NULL isn't an error in this API.
> 
> Which is okay. I dunno what should be returned from clk_round_rate() if
> clk is NULL. I would fix CLK framework, though I would like to gather
> more details.

Hmm, the common clock framwork is just one implementation of the clock
API that won't use NULL as a valid clock handle. HAVE_CLK=n is just
another implementation that does return NULL as a valid value, and
accepts that value in the other clk functions.

> Btw, I hope you also noticed this one:
> 
> http://www.spinics.net/lists/linux-serial/msg25314.html

Interesting.

Following Russel's past advise[1], the following patch on top of Heiko's
patch also fixes things for me on Octeon:

[1] https://lists.gt.net/linux/kernel/2102623

If thats an acceptable fix I'll post it properly. Thoughts?

Cheers
James

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 223ac234ddb2..e65808c482f1 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -267,6 +267,8 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
 	rate = clk_round_rate(d->clk, baud * 16);
 	if (rate < 0)
 		ret = rate;
+	else if (rate == 0)
+		ret = -ENOENT;
 	else
 		ret = clk_set_rate(d->clk, rate);
 	clk_prepare_enable(d->clk);

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