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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