netdev - RE: [PATCH 1/4] ucc_geth: Change private immrbar_virt_to

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Date:	Thu, 8 Feb 2007 15:06:25 +0800
From:	"Li Yang-r58472" <LeoLi@...escale.com>
To:	"Kumar Gala" <galak@...nel.crashing.org>
Cc:	"Tabi Timur-B04825" <timur@...escale.com>,
	<netdev@...r.kernel.org>, <linuxppc-dev@...abs.org>
Subject: RE: [PATCH 1/4] ucc_geth: Change private immrbar_virt_to_phys to generic iopa

> >>>>> If its been mapped with ioremap() you know the physical address
> >>> already
> >>>>> so why do you need iopa().
> >>>>
> >>>> That's what the original function immrbar_virt_to_phys() does.
> > We're
> >>> trying to
> >>>> get rid of it, because we thought is redundant with iopa().
> >>>>
> >>>> static inline unsigned long immrbar_virt_to_phys(volatile void *
> >>> address)
> >>>> {
> >>>> 	if ( ((u32)address >= (u32)qe_immr) &&
> >>>> 			((u32)address < ((u32)qe_immr + QE_IMMAP_SIZE))
> >>> )
> >>>> 		return (unsigned long)(address - (u32)qe_immr +
> >>>> 				(u32)get_qe_base());
> >>>> 	return (unsigned long)virt_to_phys(address);
> >>>> }
> >>>>
> >>>> get_qe_base() does a search of the OF tree the first time it's
> >>>> called.
> >>>>
> >>>> Here's the code that calls immrbar_virt_to_phys():
> >>>>
> >>>> 	out_be32(&ugeth->p_send_q_mem_reg->sqqd[i].bd_ring_base,
> >>>> 		 (u32) immrbar_virt_to_phys(ugeth->
> >>>> 					    p_tx_bd_ring[i]));
> >>>>
> >>>>
> >>>> Would it be better to replace this code with something like this:
> >>>>
> >>>> out_be32(&ugeth->p_send_q_mem_reg->sqqd[i].bd_ring_base,
> >>>> 	get_qe_base() + ((void *) ugeth->p_tx_bd_ring[i] - (void *)
> >>> qe_immr));
> >>>
> >>> No, we don't know if the BD ring is in MURAM or main memory as it
is
> >>> configurable.  iopa() is best choice to handle both case, IMHO.
> >>
> >> Does MURAM behave differently than normal memory?
> >
> > MURAM is a mmio region so it don't share the characteristic of main
> > memory that phy_addr = virt_addr - PAGE_OFFSET.  While they can
> > both be
> > mapped through page table using iopa().
> 
> Right, so when do you know if you'll be using MURAM or normal
> memory?  Why not just keep around a token that is the physical
> address at the point you make the decision of MURAM vs normal memory.

Yes, that can be a way.  But as the virt to phy mapping is only used
once, it's nothing bad to do it this way.

- Leo
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