Re: [PATCH v10 3/5] CPM/QE: use genalloc to manage CPM/QE muram

[Scott Wood <scottwood@freescale.com>]

On Wed, 2015-09-23 at 00:28 -0500, Zhao Qiang-B45475 wrote:
> On Wen, Sep 23, 2015 at 12:03 AM +0800, Wood Scott-B07421 wrote:
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, September 23, 2015 12:03 PM
> > To: Zhao Qiang-B45475
> > Cc: linux-kernel@vger.kernel.org; linuxppc-dev@lists.ozlabs.org;
> > lauraa@codeaurora.org; Xie Xiaobo-R63061; benh@kernel.crashing.org; Li
> > Yang-Leo-R58472; paulus@samba.org
> > Subject: Re: [PATCH v10 3/5] CPM/QE: use genalloc to manage CPM/QE muram
> > 
> > On Tue, 2015-09-22 at 21:20 -0500, Zhao Qiang-B45475 wrote:
> > > On Wen, Sep 23, 2015 at 8:19 AM +0800, Wood Scott-B07421 wrote:
> > > 
> > > > > > >  {
> > > > > > > - int ret;
> > > > > > > +
> > > > > > > + unsigned long start;
> > > > > > >   unsigned long flags;
> > > > > > > + unsigned long size_alloc = size; struct muram_block *entry;
> > > > > > > + int end_bit; int order = muram_pool->min_alloc_order;
> > > > > > > 
> > > > > > >   spin_lock_irqsave(&cpm_muram_lock, flags);
> > > > > > > - ret = rh_free(&cpm_muram_info, offset);
> > > > > > > + end_bit = (offset >> order) + ((size + (1UL << order) - 1)
> > > > > > > + >>
> > > > > > order);
> > > > > > > + if ((offset + size) > (end_bit << order))
> > > > > > > +         size_alloc = size + (1UL << order);
> > > > > > 
> > > > > > Why do you need to do all these calculations here?
> > > > > 
> > > > > So do it in gen_pool_fixed_alloc?
> > > > 
> > > > Could you explain why they're needed at all?
> > > 
> > > Why it does the calculations?
> > > If the min block of gen_pool is 8 bytes, and I want to allocate a
> > > Region with offset=7, size=8bytes, I actually need block 0 and block
> > > 1, And the allocation will give me block 0.
> > 
> > How can you have offset 7 if the minimum order is 2 bytes?
> 
> Offset has no relationship with minimum order, it is not decided by minimum 
> order.

All allocations begin and end on a multiple of the minimum order.

> I want to allocate a specific region with offset=7, then algo to calculate 
> the block bit.
> And I just take it for example, it is not I really need to region offset=7.

Do you really need any fixed allocations that begin on an odd address?

> So, now minimum order is 2 bytes. If offset=7, size=4bytes needed, it 
> actually allocate 6-12 to me.

Why 6-12 and not 6-10?

-Scott