linux-kernel - Re: [RFC PATCH 6/8] firmware: arm_scmi: add initial support for power protocol

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Message-ID: <d610d205-aa19-cf2f-072a-8b64c8c8be66@arm.com>
Date:   Thu, 8 Jun 2017 10:39:43 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, Roy Franz <roy.franz@...ium.com>,
        Harb Abdulhamid <harba@...eaurora.org>,
        Nishanth Menon <nm@...com>
Subject: Re: [RFC PATCH 6/8] firmware: arm_scmi: add initial support for power
 protocol



On 07/06/17 21:38, Arnd Bergmann wrote:
> On Wed, Jun 7, 2017 at 6:10 PM, Sudeep Holla <sudeep.holla@....com> wrote:
> 
>> +struct scmi_msg_resp_power_attributes {
>> +       __le16 num_domains;
>> +       __le16 reserved;
>> +       __le32 stats_addr_low;
>> +       __le32 stats_addr_high;
>> +       __le32 stats_size;
>> +} __packed;
>> +
>> +struct scmi_msg_resp_power_domain_attributes {
>> +       __le32 flags;
>> +#define SUPPORTS_STATE_SET_NOTIFY(x)   ((x) & BIT(31))
>> +#define SUPPORTS_STATE_SET_ASYNC(x)    ((x) & BIT(30))
>> +#define SUPPORTS_STATE_SET_SYNC(x)     ((x) & BIT(29))
>> +           u8 name[SCMI_MAX_STR_SIZE];
>> +} __packed;
> 
> I think it would be better to leave out the __packed here, which
> can lead to rather inefficient code. It's only really a problem when
> building with -mstrict-align, but it's better to write code in a way that
> doesn't rely on that.
> 

I assume you are referring to above structure only and not general
across all the structures ? I will have a look at this one.

>> +static int
>> +scmi_power_domain_attributes_get(struct scmi_handle *handle, u32 domain,
>> +                                struct power_dom_info *dom_info)
>> +{
>> +       int ret;
>> +       struct scmi_xfer *t;
>> +       struct scmi_msg_resp_power_domain_attributes *attr;
>> +
>> +       ret = scmi_one_xfer_init(handle, POWER_DOMAIN_ATTRIBUTES,
>> +                                SCMI_PROTOCOL_POWER, sizeof(domain),
>> +                                sizeof(*attr), &t);
>> +       if (ret)
>> +               return ret;
>> +
>> +       *(__le32 *)t->tx.buf = cpu_to_le32(domain);
>> +       attr = (struct scmi_msg_resp_power_domain_attributes *)t->rx.buf;
> 
> It seems you require a similar pattern in each caller of scmi_one_xfer_init(),
> but it seems a little clumsy to always require those casts, so maybe there
> is a nicer way to do this. How about making scmi_one_xfer_init() act
> as an allocation function and having it return the buffer or a PTR_ERR?
> 

Yes I agree it doesn't looks all nice. I have changed these few times
while developing and then thought it's better to get some suggestions. I
am open to any suggestions that will help to make these nicer.

> It also seems odd to have it named 'init' but actually allocate the scmi_xfer
> structure rather than filling a local variable that gets passed by reference.
> 

It does initialise but partially. scmi_one_xfer_get does pure allocation
while scmi_one_xfer_init initialise header variables and also tx/rx
size. But if you think it's odd, I will looks at ways to make it better.

-- 
Regards,
Sudeep