linux-kernel - Re: [PATCH] slimbus: Linux driver framework for SLIMbus.

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Message-ID: <20120604171344.GA15837@plastictigers.com>
Date:	Mon, 4 Jun 2012 13:13:44 -0400
From:	Marc Butler <marc@...stictigers.com>
To:	Sagar Dharia <sdharia@...eaurora.org>
Cc:	davidb@...eaurora.org, bryanh@...eaurora.org,
	kheitke@...eaurora.org, gclemson@...ience.com,
	broonie@...nsource.wolfsonmicro.com, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, rob@...dley.net,
	grant.likely@...retlab.ca, rob.herring@...xeda.com,
	ohad@...ery.com, gregkh@...uxfoundation.org,
	linus.walleij@...aro.org, rusty@...tcorp.com.au,
	joerg.roedel@....com, trenn@...e.de, ak@...ux.intel.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH] slimbus: Linux driver framework for SLIMbus.

On Mon, Jun 04, 2012 at 03:21:06AM -0700, Sagar Dharia wrote:
> > The enumeration slim_ch_proto is incorrect. It declares 2 transport
> > protocols which do not exist in the specification: SLIM_HARD_ISO;
> > SLIM_AUTO_ISO.
> 
> The enums are more SW representation (and not 1-1 mapping). Difference
> between HARD_ISO and AUTO_ISO with example:
> Let's say the root frequency is 24.576MHz. then all 4K family channels
> (sample rate multiple of 4K) can run isochronously, and all 11.025KHz
> channel can run with good efficiency.
> So if a client wants 11.025KHz and is does not want to do flow-control at
> this root frequency, then the client can specify AUTO_ISO to get the next
> available isochronous frequency.

I understand it is not a 1-to-1 mapping. However it *is* used as such:

 wbuf[2] = (u8)((segdist & 0xF00) >> 8) | (slc->prop.prot << 4);

which results in NEXT_DEFINE_CHANNEL messages with an invalid TP
field.

More importantly I think it makes it harder to understand the
framework. The concept of HARD_ISO and AUTO_ISO are extensions, and
should really look like such, say perhaps:

enum {
       SLIM_ISO,
       SLIM_PUSH,
       SLIM_PULL,
       SLIM_LOCKED,
       SLIM_ASYNC_SMPLX,
       SLIM_ASYNC_HALF_DUP,
       SLIM_EXT_SMPLX, 
       SLIM_EXT_HALF_DUP,
       SLIM_AUTO_ISO,
       SLIM_USER_DEF_1 = 14,
       SLIM_USER_DEF_2 = 15,
       /* extensions */
       SLIM_HARD_ISO,
       SLIM_AUTO_ISO
};       

> > b) Similarly to (a) the driver may be probed before the device has
> > been given a logical address (LA). This makes sense in the case of
> > driver that turns on the device (say via gpio) once the bus has
> > booted. However, the driver then needs to sit and poll
> > slim_get_logical_addr() until the logical address.
> This is not the case anymore.
> While taking care of the comments for RFC, I have introduced a completion
> that will be signalled when LA is given to the device. The driver can wait
> on that completion (wait_enum) instead of polling.

Yes, my mistake. The driver wouldn't have to poll if there was another
callback. So I don't see how the completion mechanism is superior: it
forces a synchronous interface to asynchronous events, or the driver
developer has to work around it.

-- 
If you wake up and you're not in pain, you know you're dead.
(Russian Proverb)

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