netdev - Re: ixp4xx_hss MAX_CHAN

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Date:	Mon, 24 Nov 2008 17:14:36 +0100
From:	Krzysztof Halasa <khc@...waw.pl>
To:	Miguel Ángel Álvarez <gotzoncabanes@...il.com>
Cc:	netdev@...r.kernel.org, linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: ixp4xx_hss MAX_CHAN_DEVICES

"Miguel Ángel Álvarez" <gotzoncabanes@...il.com> writes:

> +++ linux-2.6.26.7/drivers/net/wan/ixp4xx_hss.c	2008-11-24

> +struct physical_modes {
> +	u8 id;
> +	unsigned int frame_size;
> +	unsigned int clock_rate;
> +	u32 clock_config;
> +};

I think the clock rate shouldn't be a part of the fixed port config.
I don't know much about 4E1 configs, but in the usual case (single
physical port connected directly to the HSS) you can use many clock
and frame size configurations.

IOW I think physical mode = only signal/timeslot routing topology.
The platform code could also optionally check if the specified clock
type and rate is valid.

> +static const struct physical_modes phmodes[] = {
> +	{IXP4XX_HSS_T1, 193, 1544000, CLK42X_SPEED_1544KHZ},
> +	{IXP4XX_HSS_E1, 256, 2048000, CLK42X_SPEED_2048KHZ},
> +	{IXP4XX_HSS_2_E1, 512, 4096000, CLK42X_SPEED_4096KHZ},
> +	{IXP4XX_HSS_4_E1, 1024, 8192000, CLK42X_SPEED_8192KHZ},
> +	{0, 256, 2048000, CLK42X_SPEED_2048KHZ}
> +};

If we need different internal clock rates (most framers/multiplexers
provide their own, don't they?) then I guess we need to calculate the
required settings ourselves. I don't exactly know how do they
calculate the register but it should be easy to find out. There was no
need yet.

> +#define IXP4XX_HSS_T1     0x10
> +#define IXP4XX_HSS_E1     0x11

T1 and E1 are the same WRT hardware connection to the port.

> - How should all these changes interact with show_frame_size and
> set_frame_size?

Perhaps the platform code should initialize the value and then check
changes for validity. Only matters with G.704 framers I think.
Otherwise the user should be able to select anything.

> - I am a bit lost with MAX_CHANNELS and MAX_CHAN_DEVICES... Which are
> the differences between both?

MAX_CHANNELS = (currenly) 32 = max for single channel (32 E1
channels).
MAX_CHAN_DEVICES = limit of /dev/hssXchY nodes (for one port).

> - As MAX_CHANNELS and MAX_CHAN_DEVICES should not be set by defines, I
> am going to alloc memory for chan_devices... I am going to do it in
> init_one... Is it OK?.

MAX_CHANNELS, I think so.
MAX_CHAN_DEVICES isn't directly related.

> My first intention for all this is to set HSS into MVIP mode and have
> 4 HDLC channels in a packetized mode.
> - How could I set this MVIP mode?
> - How could I interface with generic HDLC so that hss_hdlc_xmit sends
> the data for each stream to a different FIFO?

The HSS driver should initialize MVIP based on platform's
physical_config value, then it would have to register 4 HDLC devices.

The HDLC part (not the channelized one) should be quite trivial.
I think we now need the HSS HDLC driver upstream, will look at this.
-- 
Krzysztof Halasa
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