From: John Garry <john.garry@huawei.com>
To: Will Deacon <will.deacon@arm.com>
Cc: "zhichang.yuan" <yuanzhichang@hisilicon.com>,
<mark.rutland@arm.com>, <devicetree@vger.kernel.org>,
<lorenzo.pieralisi@arm.com>, <benh@kernel.crashing.org>,
<minyard@acm.org>, <arnd@arndb.de>, <catalin.marinas@arm.com>,
<gabriele.paoloni@huawei.com>, <zhichang.yuan02@gmail.com>,
<liviu.dudau@arm.com>, <linux-kernel@vger.kernel.org>,
<xuwei5@hisilicon.com>, <linuxarm@huawei.com>, <olof@lixom.net>,
<robh+dt@kernel.org>, <zourongrong@gmail.com>,
<linux-serial@vger.kernel.org>, <linux-pci@vger.kernel.org>,
<bhelgaas@google.com>, <kantyzc@163.com>,
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH V5 1/3] ARM64 LPC: Indirect ISA port IO introduced
Date: Tue, 8 Nov 2016 17:05:50 +0000 [thread overview]
Message-ID: <ecf81900-8116-2ef7-8ebb-e5739cc91de7@huawei.com> (raw)
In-Reply-To: <20161108164948.GG20591@arm.com>
On 08/11/2016 16:49, Will Deacon wrote:
> On Tue, Nov 08, 2016 at 04:33:44PM +0000, John Garry wrote:
>> On 08/11/2016 16:12, Will Deacon wrote:
>>> On Tue, Nov 08, 2016 at 11:47:07AM +0800, zhichang.yuan wrote:
>>>> +static inline void arm64_set_extops(struct extio_ops *ops)
>>>> +{
>>>> + if (ops)
>>>> + WRITE_ONCE(arm64_extio_ops, ops);
>>>
>>> Why does this need to be WRITE_ONCE? You don't have READ_ONCE on the reader
>>> side. Also, what if multiple drivers want to set different ops for distinct
>>> address ranges?
>>
>> I think that the idea here is that we only have possibly one master in the
>> system which offers indirectIO backend, so another one could not possibly
>> re-set this value.
>
> Why is that assumption valid, and why does WRITE_ONCE help there? It's not
> ONCE as in WARN_ONCE, more ONCE as in exactly-once-per-invocation.
It's only valid based on the inherent assumption that all indirectIO is
redirected to one backend master, i.e. LPC driver.
Anyway, right, I don't think that WRITE_ONCE is correct. Zhichang was
looking for something which would only allow the pointer to be written
once ever.
>
>>>> diff --git a/arch/arm64/kernel/extio.c b/arch/arm64/kernel/extio.c
>>>> new file mode 100644
>>>> index 0000000..647b3fa
>>>> --- /dev/null
>>>> +++ b/arch/arm64/kernel/extio.c
>>>> @@ -0,0 +1,27 @@
>>>> +/*
>>>> + * Copyright (C) 2016 Hisilicon Limited, All Rights Reserved.
>>>> + * Author: Zhichang Yuan <yuanzhichang@hisilicon.com>
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License version 2 as
>>>> + * published by the Free Software Foundation.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful,
>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>>> + * GNU General Public License for more details.
>>>> + *
>>>> + * You should have received a copy of the GNU General Public License
>>>> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
>>>> + */
>>>> +
>>>> +#include <linux/io.h>
>>>> +
>>>> +struct extio_ops *arm64_extio_ops;
>>>> +
>>>> +
>>>> +BUILD_EXTIO(b, u8)
>>>> +
>>>> +BUILD_EXTIO(w, u16)
>>>> +
>>>> +BUILD_EXTIO(l, u32)
>>>
>>> Is there no way to make this slightly more generic, so that it can be
>>> re-used elsewhere? For example, if struct extio_ops was common, then
>>> you could have the singleton (which maybe should be an interval tree?),
>>> type definition, setter function and the BUILD_EXTIO invocations
>>> somewhere generic, rather than squirelled away in the arch backend.
>>>
>> The concern would be that some architecture which uses generic higher-level
>> ISA accessor ops, but have IO space, could be affected.
>
> You're already adding a Kconfig symbol for this stuff, so you can keep
> that if you don't want it on other architectures. I'm just arguing that
> plumbing drivers directly into arch code via arm64_set_extops is not
> something I'm particularly fond of, especially when it looks like it
> could be avoided with a small amount of effort.
We'll check this.
Cheers,
John
>
> Will
>
> .
>
next prev parent reply other threads:[~2016-11-08 17:06 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-08 3:47 [PATCH V5 0/3] ARM64 LPC: legacy ISA I/O support zhichang.yuan
2016-11-08 3:47 ` [PATCH V5 1/3] ARM64 LPC: Indirect ISA port IO introduced zhichang.yuan
2016-11-08 12:03 ` Mark Rutland
2016-11-08 16:09 ` Arnd Bergmann
2016-11-08 16:15 ` Arnd Bergmann
2016-11-08 23:16 ` Benjamin Herrenschmidt
2016-11-10 8:33 ` zhichang.yuan
2016-11-10 11:22 ` Mark Rutland
2016-11-10 19:32 ` Benjamin Herrenschmidt
2016-11-11 10:07 ` zhichang.yuan
2016-11-18 9:20 ` Arnd Bergmann
2016-11-18 11:12 ` zhichang.yuan
2016-11-18 11:38 ` Arnd Bergmann
2016-11-21 12:58 ` John Garry
2016-11-08 16:12 ` Will Deacon
2016-11-08 16:33 ` John Garry
2016-11-08 16:49 ` Will Deacon
2016-11-08 17:05 ` John Garry [this message]
2016-11-08 22:35 ` Arnd Bergmann
2016-11-09 11:29 ` John Garry
2016-11-09 21:33 ` Arnd Bergmann
2016-12-22 8:15 ` Ming Lei
2016-12-23 1:43 ` zhichang.yuan
2016-12-23 7:24 ` Ming Lei
2017-01-06 11:43 ` Arnd Bergmann
2016-11-08 3:47 ` [PATCH V5 2/3] ARM64 LPC: Add missing range exception for special ISA zhichang.yuan
2016-11-08 5:17 ` kbuild test robot
2016-11-08 5:27 ` kbuild test robot
2016-11-08 11:49 ` Mark Rutland
2016-11-08 16:19 ` Arnd Bergmann
2016-11-08 17:10 ` Mark Rutland
2016-11-09 13:54 ` One Thousand Gnomes
2016-11-09 14:51 ` Gabriele Paoloni
2016-11-09 21:38 ` Arnd Bergmann
2016-11-14 11:11 ` One Thousand Gnomes
2016-11-18 9:22 ` Arnd Bergmann
2016-11-08 23:12 ` Benjamin Herrenschmidt
2016-11-09 11:20 ` Mark Rutland
2016-11-10 7:08 ` Benjamin Herrenschmidt
2016-11-09 11:39 ` liviu.dudau
2016-11-09 16:16 ` Gabriele Paoloni
2016-11-09 16:50 ` liviu.dudau
2016-11-10 6:24 ` zhichang.yuan
2016-11-10 16:06 ` Gabriele Paoloni
2016-11-11 10:37 ` liviu.dudau
2016-11-08 3:47 ` [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on Hip06 zhichang.yuan
2016-11-08 6:11 ` kbuild test robot
2016-11-08 16:24 ` Arnd Bergmann
2016-11-09 12:10 ` Gabriele Paoloni
2016-11-09 21:34 ` Arnd Bergmann
2016-11-10 6:40 ` zhichang.yuan
2016-11-10 9:12 ` Arnd Bergmann
2016-11-10 12:36 ` zhichang.yuan
2016-11-18 11:46 ` Arnd Bergmann
2016-11-10 15:36 ` Gabriele Paoloni
2016-11-10 16:07 ` Arnd Bergmann
2016-11-11 10:09 ` zhichang.yuan
2016-11-11 10:48 ` liviu.dudau
2016-11-11 13:39 ` Gabriele Paoloni
2016-11-11 14:45 ` liviu.dudau
2016-11-11 15:53 ` Gabriele Paoloni
2016-11-11 18:16 ` liviu.dudau
2016-11-14 8:26 ` Gabriele Paoloni
2016-11-14 11:26 ` liviu.dudau
2016-11-18 10:17 ` Arnd Bergmann
2016-11-18 12:07 ` Gabriele Paoloni
2016-11-18 12:24 ` Arnd Bergmann
2016-11-18 12:53 ` Gabriele Paoloni
2016-11-18 13:42 ` Arnd Bergmann
2016-11-18 16:18 ` Gabriele Paoloni
2016-11-18 16:34 ` Arnd Bergmann
2016-11-18 17:03 ` Gabriele Paoloni
2016-11-23 14:16 ` Arnd Bergmann
2016-11-23 15:22 ` Gabriele Paoloni
2016-11-23 17:07 ` Arnd Bergmann
2016-11-23 23:23 ` Arnd Bergmann
2016-11-24 9:12 ` zhichang.yuan
2016-11-24 10:24 ` Arnd Bergmann
2016-11-25 8:46 ` Gabriele Paoloni
2016-11-25 12:03 ` Arnd Bergmann
2016-11-25 16:27 ` Gabriele Paoloni
2016-11-11 16:54 ` zhichang.yuan
2016-11-14 11:06 ` One Thousand Gnomes
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