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

From: Laura Abbott
Date: Tue Aug 25 2015 - 00:15:01 EST

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

On 08/24/2015 02:31 AM, Zhao Qiang wrote:

+ of_node_put(np);
+ return ret;
+ * qe_muram_alloc - allocate the requested size worth of multi-user
+ * @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_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.


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