linux-kernel - Re: [PATCH v7 1/2] serial: sc16is7xx

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Message-ID: <alpine.LRH.2.03.1404251019300.2893@frank.harvard.edu>
Date:	Fri, 25 Apr 2014 10:24:30 -0400 (EDT)
From:	Charles Coldwell <coldwell@...il.com>
To:	Jon Ringle <jon@...gle.org>
cc:	Charles Coldwell <coldwell@...il.com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Alexander Shiyan <shc_work@...l.ru>,
	Jon Ringle <jringle@...dpoint.com>
Subject: Re: [PATCH v7 1/2] serial: sc16is7xx

On Fri, 25 Apr 2014, Jon Ringle wrote:

> On Fri, Apr 25, 2014 at 9:44 AM, Charles Coldwell <coldwell@...il.com> wrote:
> > On Fri, 25 Apr 2014, Charles Coldwell wrote:
> >
> >> On Thu, 24 Apr 2014, jon@...gle.org wrote:
> >>
> >> > diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> >>
> >> Isn't this a lot of duplication?
> >
> > Actually, the whole thing seems like duplication to me.
> 
> The fact that we need to reach over the SPI/I2C bus makes a big
> difference in the way access is handled.
> 
> To achieve acceptable throughput, it is necessary to use threaded irq
> and also bulk i2c transfers for RX and TX using
> regmap_raw_{read,write}() to optimize the use of the i2c bus.

Fair enough, but the 8250 framework does allow you to insert your own
irq service routine. "serial8250_default_handle_irq" is the default
(unsurprisingly), but if the uart_port has a non-NULL "handle_irq"
method it will be faithfully copied into the uart_8250_port
"handle_irq" method in 8250_core.c:early_serial_setup.

> This is not a good fit for 8250.

If that's really true, then I would say it argues in favor of a
revision of the 8250 code.  Certainly, this is not the last time that
a 16550-compatible UART will appear on a non-PCI, non-ISA bus.

-- 
Charles M. Coldwell, W1CMC
"Turn on, log in, tune out"
Somerville, Massachusetts, New England (FN42kj)

GPG ID:  852E052F
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