From: Zhao Qiang <qiang.zhao@freescale.com>
To: Laura Abbott <labbott@redhat.com>, Scott Wood <scottwood@freescale.com>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        "lauraa@codeaurora.org" <lauraa@codeaurora.org>,
        Xiaobo Xie <X.Xie@freescale.com>,
        "benh@kernel.crashing.org" <benh@kernel.crashing.org>,
        Li Leo <LeoLi@freescale.com>, "paulus@samba.org" <paulus@samba.org>
Subject: RE: [PATCH v6 3/3] qe_common: add qe_muram_ functions to manage muram
Thread-Topic: [PATCH v6 3/3] qe_common: add qe_muram_ functions to manage
 muram
Thread-Index: AQHQ3lE08qg+K0DuDEa/oy40LAO0yp4bzaWAgAA3LDCAABe8AIAAMajw
Date: Tue, 25 Aug 2015 07:19:17 +0000
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On 08/25/2015 12:15 PM, Laura Abbott wrote
> -----Original Message-----
> From: Laura Abbott [mailto:labbott@redhat.com]
> Sent: Tuesday, August 25, 2015 12:15 PM
> To: Zhao Qiang-B45475; Wood Scott-B07421
> 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 v6 3/3] qe_common: add qe_muram_ functions to manage
> muram
> 
> On 08/24/2015 08:03 PM, Zhao Qiang wrote:
> >
> >> -----Original Message-----
> >> From: Laura Abbott [mailto:labbott@redhat.com]
> >> Sent: Tuesday, August 25, 2015 7:32 AM
> >> To: Zhao Qiang-B45475; Wood Scott-B07421
> >> 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 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.
> 

The workaround works for non alignment allocation, but for alignment allocation,
It need to align bytes to addr 0, offsetting the gen_pool_add maybe make wrong alignment
.

> 
> Thanks,
> Laura
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