On Sun, Mar 26, 2017 at 11:22:57AM +0200, Geert Uytterhoeven wrote:

Hi Russell, Sjoerd,

On Fri, Mar 24, 2017 at 5:42 PM, Russell King - ARM Linux
[off-list ref] wrote:

quoted

On Fri, Mar 24, 2017 at 05:26:32PM +0100, Sjoerd Simons wrote:

quoted

When testing on a Renesas board with the PL010 serial driver enabled
serial output broke. Turns out the minor device numbers for both
drivers happen to overlap, causing whichever driver happened to be the
second one to register to fail.

How the **** has the SH serial driver ended up with overlapping device
numbers?

Interesting...

quoted

What happened to our maintained list of allocated major/minor device
numbers, which is supposed to stop crap like this happening?

AMBA PL010 has been assigned major 204, minors 16..31,
SCI has been assigned major 204, minors 8..11.

Over the years, Renesas SoCs have been gaining more and more serial
ports, leading to

    #define SCI_NPORTS CONFIG_SERIAL_SH_SCI_NR_UARTS

with CONFIG_SERIAL_SH_SCI_NR_UARTS=20 in shmobile_defconfig and
multi_v7_defconfig (although the maximum value on any supported SoC is 18).

But once the value becomes 5 or more, it starts overflowing into the ttyFWx
and ttyAMx space.

How to solve this?
Time for the serial subsystem to switch to dynamic minors, and get rid of the
what-is-your-serial-port-called-again-on-this-platform
multi-million-euro question?

Yes, please, we need to do that.  Let's provide a build option for it,
like USB has had for over a decade.  If it's enabled, it's all dynamic,
if not, the "old style" ones are used.  Then we don't accept any new
reservations, making new drivers use the dynamic number, and over a long
time, all should be good.

thanks,

greg k-h