Re: [PATCH V7 1/3] genalloc:support memory-allocation with bytes-alignment to genalloc

[Scott Wood <scottwood@freescale.com>]

On Tue, 2015-09-01 at 21:10 -0500, Zhao Qiang-B45475 wrote:
> On Wed, 2015-09-02 at 08:38AM +0800, Wood Scott-B07421 wrote:
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, September 02, 2015 8:30 AM
> > 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 V7 1/3] genalloc:support memory-allocation with
> > bytes-alignment to genalloc
> > 
> > On Mon, 2015-08-31 at 16:58 +0800, Zhao Qiang wrote:
> > > Bytes alignment is required to manage some special RAM, so add
> > > gen_pool_first_fit_align to genalloc, meanwhile add
> > > gen_pool_alloc_data to pass data to gen_pool_first_fit_align(modify
> > > gen_pool_alloc as a wrapper)
> > > 
> > > Signed-off-by: Zhao Qiang <qiang.zhao@freescale.com>
> > > ---
> > > Changes for v6:
> > >       - patches set v6 include a new patch because of using
> > >       - genalloc to manage QE MURAM, patch 0001 is the new
> > >       - patch, adding bytes alignment for allocation for use.
> > > Changes for v7:
> > >       - cpm muram also need to use genalloc to manage, it has
> > >         a function to reserve a specific region of muram,
> > >         add offset to genpool_data for start addr to be allocated.
> > 
> > This seems to be describing more than just the changes in this patch.
> > What does also handling cpm have to do with this patch?  Are you adding
> > support for reserving a specific region in this patch?  I don't see it,
> > and in any case it should go in a different patch.
> 
> Yes, I added. The code below can support the function.
>       offset_bit = (alignment->offset + (1UL << order) - 1) >> order;
>       return bitmap_find_next_zero_area(map, size, start + offset_bit, nr,
>                         align_mask);
>
> CPM has an function cpm_muram_alloc_fixed, needing to allocate muram from a
> Specific offset. So I add the code and add offset to struct data.

I thought the offset was related to the previous discussion of checking for 
allocation failure.  Are you using it to implement alloc_fixed()?  If so, 
please don't.  Besides the awkward implementation (what does it logically 
have to do with gen_pool_first_fit_align?), it does not appear to be correct -
- what happens with multiple chunks?  What happens if part of the region the 
caller is trying to reserve is already taken?  Implement a proper function to 
reserve a fixed genalloc region.

> This patch is the first patch of this patch set, so I explain what changes 
> about
> Set v7 and why I add support for reserving a specific region in this patch.

If you want to provide commentary that covers the entire patchset, use a 
cover letter.

> > > +/*
> > > + *  gen_pool data descriptor for gen_pool_first_fit_align.
> > > + */
> > > +struct genpool_data_align {
> > > +     int align;              /* alignment by bytes for starting
> > address */
> > > +     unsigned long offset;   /* the offset of allocation start addr*/
> > > +};
> > 
> > The offset belongs on the caller side, not here.
> 
> So, how do I pass offset to gen_pool_alloc_data or pool->algo?

You don't.

-Scott