Re: [PATCH v6 3/3] qe_common: add qe_muram_ functions to manage muram

[Laura Abbott]

On 08/24/2015 08:03 PM, Zhao Qiang wrote:
> > -----Original Message-----
> > From: Laura Abbott [mailto:labbott@xxxxxxxxxx]
> > Sent: Tuesday, August 25, 2015 7:32 AM
> > To: Zhao Qiang-B45475; Wood Scott-B07421
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > lauraa@xxxxxxxxxxxxxx; Xie Xiaobo-R63061; benh@xxxxxxxxxxxxxxxxxxx; Li
> > Yang-Leo-R58472; paulus@xxxxxxxxx
> > Subject: Re: [PATCH v6 3/3] qe_common: add qe_muram_ functions to manage
> > muram
> >
> > On 08/24/2015 02:31 AM, Zhao Qiang wrote:
> >
> >
> > > +out:
> > > +	of_node_put(np);
> > > +	return ret;
> > > +}
> > > +
> > > +/**
> > > + * qe_muram_alloc - allocate the requested size worth of multi-user
> > > +ram
> > > + * @size: number of bytes to allocate
> > > + * @align: requested alignment, in bytes
> > > + *
> > > + * This function returns an offset into the muram area.
> > > + * Use qe_dpram_addr() to get the virtual address of the area.
> > > + * Use qe_muram_free() to free the allocation.
> > > + */
> > > +unsigned long qe_muram_alloc(unsigned long size, unsigned long align)
> > > +{
> > > +	unsigned long start;
> > > +	unsigned long flags;
> > > +	struct muram_block *entry;
> > > +
> > > +	spin_lock_irqsave(&qe_muram_lock, flags);
> > > +	muram_pool_data.align = align;
> > > +	start = gen_pool_alloc(muram_pool, size);
> >
> > The advantage of creating gen_pool_alloc_data was so that you could pass
> > in the align automatically without having to modify the structure.
> > Is there a reason you aren't using that?
> >
> > > +	memset(qe_muram_addr(start), 0, size);
> >
> > There doesn't seem to be a check for allocation failure from the
> > gen_alloc.
>
> gen_pool_alloc will return 0 if there is error, but if the address returned is
> just 0x0, it can't distinguish it is address or error.

Yes, that's a bad limitation of gen_pool. Maybe one day that will get fixed.
In a previous out of tree driver, I worked around this by offsetting the
gen_pool_add by a constant so any return value was non-zero and out of memory
was zero and then subtracting the constant off of the return value. Not sure
if that's better or worse than just fixing gen_alloc.
 
> > > +	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
> > > +	if (!entry)
> > > +		goto out;
> > > +	entry->start = start;
> > > +	entry->size = size;
> > > +	list_add(&entry->head, &muram_block_list);
> >
> > What's the point of keeping the block list anyway? It's used only in this
> > file and it only seems to duplicate what gen_alloc is doing internally.
> > Is there some lookup functionality you still need? Could you use a
> > gen_alloc API to do so?
>
> I need to record the size when allocation, so when free the block, I can get
> The right size for the block, and pass the right size to
> gen_pool_free(struct gen_pool *pool, unsigned long addr, size_t size).

Yes, I see now what you are doing.
 
> > Thanks,
> > Laura
> Thanks
> Zhao

Thanks,
Laura
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