linux-kernel - RE: [PATCH v6 3/3] qe_common: add qe_muram

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Date:	Tue, 25 Aug 2015 03:03:09 +0000
From:	Zhao Qiang <qiang.zhao@...escale.com>
To:	Laura Abbott <labbott@...hat.com>,
	Scott Wood <scottwood@...escale.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	Xiaobo Xie <X.Xie@...escale.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	Li Leo <LeoLi@...escale.com>,
	"paulus@...ba.org" <paulus@...ba.org>
Subject: RE: [PATCH v6 3/3] qe_common: add qe_muram_ functions to manage muram


> -----Original Message-----
> From: Laura Abbott [mailto:labbott@...hat.com]
> Sent: Tuesday, August 25, 2015 7:32 AM
> To: Zhao Qiang-B45475; Wood Scott-B07421
> Cc: linux-kernel@...r.kernel.org; linuxppc-dev@...ts.ozlabs.org;
> lauraa@...eaurora.org; Xie Xiaobo-R63061; benh@...nel.crashing.org; Li
> Yang-Leo-R58472; paulus@...ba.org
> 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.

> 
> > +	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).

> 
> 
> Thanks,
> Laura
Thanks 
Zhao
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