linux-kernel - Re: [RFC 3/3] mailbox: pl320: Introduce common API driver

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Date:	Mon, 29 Apr 2013 12:06:03 -0500
From:	Mark Langsdorf <mark.langsdorf@...xeda.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
CC:	Suman Anna <s-anna@...com>, Jassi Brar <jassisinghbrar@...il.com>,
	"Loic PALLARDY (loic.pallardy@...com)" <loic.pallardy@...com>,
	Arnd Bergmann <arnd@...db.de>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Andy Green <andy.green@...aro.org>
Subject: Re: [RFC 3/3] mailbox: pl320: Introduce common API driver

On 04/29/2013 11:57 AM, Jassi Brar wrote:
> On 29 April 2013 22:14, Suman Anna <s-anna@...com> wrote:
>> On 04/27/2013 01:14 PM, jassisinghbrar@...il.com wrote:
>>> From: Jassi Brar <jaswinder.singh@...aro.org>
>>> Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
>>> ---
>>>  drivers/cpufreq/highbank-cpufreq.c       |   22 +++-
>>>  drivers/mailbox/Makefile                 |    2 +-
>>>  drivers/mailbox/{pl320-ipc.c => pl320.c} |  194 ++++++++++++++++--------------
>>>  include/linux/pl320-ipc.h                |   17 ---
>>>  4 files changed, 125 insertions(+), 110 deletions(-)
>>>  rename drivers/mailbox/{pl320-ipc.c => pl320.c} (51%)
>>>  delete mode 100644 include/linux/pl320-ipc.h
>>>
>>> diff --git a/drivers/cpufreq/highbank-cpufreq.c b/drivers/cpufreq/highbank-cpufreq.c
>>> index 3118b87..5c057e0 100644
>>> --- a/drivers/cpufreq/highbank-cpufreq.c
>>> +++ b/drivers/cpufreq/highbank-cpufreq.c
>>> @@ -19,7 +19,7 @@
>>>  #include <linux/cpu.h>
>>>  #include <linux/err.h>
>>>  #include <linux/of.h>
>>> -#include <linux/pl320-ipc.h>
>>> +#include <linux/mailbox_client.h>
>>>  #include <linux/platform_device.h>
>>>
>>>  #define HB_CPUFREQ_CHANGE_NOTE       0x80000001
>>> @@ -29,8 +29,26 @@
>>>  static int hb_voltage_change(unsigned int freq)
>>>  {
>>>       u32 msg[HB_CPUFREQ_IPC_LEN] = {HB_CPUFREQ_CHANGE_NOTE, freq / 1000000};
>>> +     struct ipc_client cl;
>>> +     int ret = -ETIMEDOUT;
>>> +     void *chan;
>>>
>>> -     return pl320_ipc_transmit(msg);
>>> +     cl.rxcb = NULL;
>>> +     cl.txcb = NULL;
>>> +     cl.tx_block = true;
>>> +     cl.tx_tout = 1000; /* 1 sec */
>>> +     cl.cntlr_data = NULL;
>>> +     cl.knows_txdone = false;
>>> +     cl.chan_name = "pl320:A9_to_M3";
>>> +
>>> +     chan = ipc_request_channel(&cl);
>>> +
>>> +     if (ipc_send_message(chan, (void *)msg))
>>> +             ret = msg[1]; /* PL320 updates buffer with FIFO after ACK */
>>> +
>>> +     ipc_free_channel(chan);
>>
>> I think I understand why you have done this, but do you really want to
>> request and free every time in the highbank cpufreq driver?
>>
> Exactly my aim - make the API light enough to enable the client to
> use-and-throw. And also because the channel are exclusively assigned,
> acquire a channel only for as long as you need it.

Do you have any numbers on the performance impact? Our cpufreq
transition throughput is bad enough without adding additional delays.

--Mark Langsdorf
Calxeda, Inc.

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