linux-kernel - Re: [PATCH] IPC driver for Intel Mobile Internet Device (MID) platforms

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Date:	Thu, 22 Apr 2010 14:16:11 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alan Cox <alan@...ux.intel.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, Sreedhara DS <sreedhara.ds@...el.com>
Subject: Re: [PATCH] IPC driver for Intel Mobile Internet Device (MID)
 platforms

> __packed, please.  (I've requested that this be added to checkpatch,
> but Mr Checkpatch is asleep).

Done


> > +static inline int busy_loop(void) /* Wait till scu status is busy */
> > +{
> > +	u32 status = 0;
> > +	u32 loop_count = 0;
> > +
> > +	status = __raw_readl(IPC_STATUS_REG);
> > +	while (status & 1) {
> > +		udelay(1); /* scu processing time is in few u secods */
> > +		status = __raw_readl(IPC_STATUS_REG);
> > +		loop_count++;
> > +		/* break if scu doesn't reset busy bit after huge retry */
> > +		if (loop_count > 100000)
> > +			return -ETIMEDOUT;

> This function has seven-odd callsites and is waaaaaaaay to fat and slow
> to be inlined.

Looking at the asm I'm not convinced.


> > +	if (id == IPC_CMD_PCNTRL_R) { /* Read rbuf */
> > +		/* Workaround: values are read as 0 without memcpy_fromio */
> > +		memcpy_fromio(cbuf, IPC_READ_BUFFER, 16);
> 
> Should we still be doing this if busy_loop() failed?
> 
> (Lots of dittoes on this question)

Does no harm

> > +}
> 
> I wonder if this function would look better if cbuf had type u16[],

No - we do byte aligned access to it. and cbuf[offset + 1.5] is sadly not
supported by C (although I suspect you can make it work in C++ ;))

> > +	mutex_lock(&ipclock);
> > +	if (ipcdev.pdev == NULL) {
> 
> This check happens a lot.  Can it really happen?

Yes.

> I think mailbox_base could/should have had type `struct
> fw_update_mailbox __iomem *'.  ioremap_nocache() should handle that
> cleanly, and this cast goes away.

Definitely - and the rest them cleans up by magic

Alan
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