linux-kernel - Re: [PATCH v5 2/8] firmware: add support for ARM System Control and Power Interface(SCPI) protocol

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Date:	Wed, 29 Jul 2015 16:49:34 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Punit Agrawal <Punit.Agrawal@....com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Kevin Hilman <khilman@...nel.org>
Subject: Re: [PATCH v5 2/8] firmware: add support for ARM System Control and
 Power Interface(SCPI) protocol

On Wed, Jul 29, 2015 at 2:08 PM, Sudeep Holla <sudeep.holla@....com> wrote:
> On 29/07/15 09:05, Jassi Brar wrote:
>
>>
>>> +static int scpi_probe(struct platform_device *pdev)
>>> +{
>>> +       int count, idx, ret;
>>> +       struct resource res;
>>> +       struct scpi_chan *scpi_chan;
>>> +       struct device *dev = &pdev->dev;
>>> +       struct device_node *np = dev->of_node;
>>> +
>>> +       scpi_info = devm_kzalloc(dev, sizeof(*scpi_info), GFP_KERNEL);
>>> +       if (!scpi_info)
>>> +               return -ENOMEM;
>>> +
>>> +       count = of_count_phandle_with_args(np, "mboxes", "#mbox-cells");
>>> +       if (count < 0) {
>>> +               dev_err(dev, "no mboxes property in '%s'\n",
>>> np->full_name);
>>> +               return -ENODEV;
>>> +       }
>>> +
>>> +       scpi_chan = devm_kcalloc(dev, count, sizeof(*scpi_chan),
>>> GFP_KERNEL);
>>> +       if (!scpi_chan)
>>> +               return -ENOMEM;
>>> +
>>> +       for (idx = 0; idx < count; idx++) {
>>> +               resource_size_t size;
>>> +               struct scpi_chan *pchan = scpi_chan + idx;
>>> +               struct mbox_client *cl = &pchan->cl;
>>> +               struct device_node *shmem = of_parse_phandle(np, "shmem",
>>> idx);
>>> +
>>> +               if (of_address_to_resource(shmem, 0, &res)) {
>>> +                       dev_err(dev, "failed to get SCPI payload mem
>>> resource\n");
>>> +                       ret = -EINVAL;
>>> +                       goto err;
>>> +               }
>>> +
>>> +               size = resource_size(&res);
>>> +               pchan->rx_payload = devm_ioremap(dev, res.start, size);
>>> +               if (!pchan->rx_payload) {
>>> +                       dev_err(dev, "failed to ioremap SCPI payload\n");
>>> +                       ret = -EADDRNOTAVAIL;
>>> +                       goto err;
>>> +               }
>>> +               pchan->tx_payload = pchan->rx_payload + (size >> 1);
>>> +
>>> +               cl->dev = dev;
>>> +               cl->rx_callback = scpi_handle_remote_msg;
>>> +               cl->tx_prepare = scpi_tx_prepare;
>>> +               cl->tx_block = true;
>>> +               cl->tx_tout = 50;
>>> +               cl->knows_txdone = false; /* controller can ack */
>>>
>>   This is the cause of your problems that you think should be solved by
>> using hrtimer.
>>
>
> Ah sorry, it's stupid mistake on my part while writing the comment. It
> should have been controller can't ack, fixed locally now thanks for
> pointing it out.
>
No, I am talking about code, not the comment.

>>   Controller may or may not (like MHU) set txdone_irq. However every
>> scpi command (struct scpi_ops members) is replied to as a response
>> packet reporting success or failure.
>
>
> No that's not true, I have already mentioned that couple of times in the
> other thread. It's just wrong comment here which went unnoticed from
> day#1, sorry for that.
>
>> So the client should set 'knows_txdone' to be true unless it is told
>> the controller on that platform supports txdone_irq (what you call
>> 'ack').
>>
> I got the concept but SCP can't ack via protocol, protocol has no such
> provision and it sets flags in MHU status register.
>
You either don't get the concept of TXDONE_BY_ACK  or deliberately
overlook my point.

Assuming the former, let me explain. When a client receives a
response, it can be sure that the request has already been read by the
remote. If the protocol specifies every request has some response, the
client should assert 'knows_txdone' and call mbox_client_txdone() upon
receiving a reply packet.
   So I said,  cl->knows_txdone = false;   is the root of problems you
report. If you fix that, the performance should be even better than
using hrtimer.

-Jassi
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