problem in serial_ns16550.c

[Sascha Hauer]

On Wed, Aug 03, 2011 at 07:35:18PM +0400, 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.

Ok, then we have to check for the existence of plat->reg_read/write
first. If the exist, we have to skip further IORESOURCE_MEM_xBIT checks.
If they don't exist we do whatever IORESOURCE_MEM_xBIT indicates.

That only leaves the problem that if a user registers a ns16550 driver
without reg_read/write and does not care about resource types either
the driver defaults to 8 bit mmio accesses, but I think we can live with
that.

Sascha



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