Re: problem in serial_ns16550.c - Jean-Christophe PLAGNIOL-VILLARD

From: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
To: Antony Pavlov <antonynpavlov@gmail.com>
Cc: barebox <barebox@lists.infradead.org>
Subject: Re: problem in serial_ns16550.c
Date: Wed, 3 Aug 2011 18:35:14 +0200	[thread overview]
Message-ID: <20110803163514.GD24730@game.jcrosoft.org> (raw)
In-Reply-To: <CAA4bVAGcGr9Xv1RTMBbzYDxhcq+xrUeZCCvDJMDZ04cjVsPhZw@mail.gmail.com>

On 19:35 Wed 03 Aug     , Antony Pavlov wrote:
> Hi!
> 
> IMHO there is a problem in ns16550_probe() (see
> drivers/serial/serial_ns16550.c:243).
> 
> There is the construction:
> ------
> if (!(dev->resource[0].flags & IORESOURCE_MEM_TYPE_MASK) &&
>             ((plat->reg_read == NULL) || (plat->reg_write == NULL)))
>                 return -EINVAL;
> ------
> 
> Imagine creation of typical serial port:
> ------
> static struct NS16550_plat plat = {
>         .clock = 1843200,
> };
> 
> ...
> 
> add_ns16550_device(-1, UART_ADDR, 8, IORESOURCE_MEM_8BIT, &plat);
> ------
> 
> Here we have plat.reg_read == NULL, plat.reg_write == NULL.
> Usage of add_ns16550_device will make
> dev->resource[0].flags & IORESOURCE_MEM_TYPE_MASK == IORESOURCE_MEM_8BIT.
> 
> But take into account this (see include/linux/ioport.h):
> ------
> #define IORESOURCE_MEM_TYPE_MASK        (3<<3)
> #define IORESOURCE_MEM_8BIT             (0<<3)
> ------
> 
> So IORESOURCE_MEM_8BIT == 0 (sic!)
> 
> A son tour, !(dev->resource[0].flags & IORESOURCE_MEM_TYPE_MASK) give
> true, if flags select IORESOURCE_MEM_8BIT.
> 
> As a result, if add_ns16550_device() take IORESOURCE_MEM_8BIT, and
> plat->reg_read == NULL, plat->reg_write == NULL then ns16550_probe()
> will return -EINVAL.
yeah we can drop the check simply

Best Regards,
J.

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