linux-kernel - Re: [PATCH 1/2] mailbox: pcc: Add processing platform notification for slave subspaces

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Date:   Fri, 3 Mar 2023 11:07:45 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     "lihuisong (C)" <lihuisong@...wei.com>
Cc:     robbiek@...ghtlabs.com, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, rafael@...nel.org,
        rafael.j.wysocki@...el.com, wanghuiqiang@...wei.com,
        zhangzekun11@...wei.com, wangxiongfeng2@...wei.com,
        tanxiaofei@...wei.com, guohanjun@...wei.com, xiexiuqi@...wei.com,
        wangkefeng.wang@...wei.com, huangdaode@...wei.com
Subject: Re: [PATCH 1/2] mailbox: pcc: Add processing platform notification
 for slave subspaces

On Fri, Mar 03, 2023 at 09:50:00AM +0800, lihuisong (C) wrote:
> 
> 在 2023/3/2 21:52, Sudeep Holla 写道:
> > On Thu, Mar 02, 2023 at 09:57:35AM +0800, lihuisong (C) wrote:
> > > 在 2023/3/1 21:24, Sudeep Holla 写道:
> > [...]
> > 
> > > > +static bool pcc_mbox_cmd_complete_check(struct pcc_chan_info *pchan)
> > > > +{
> > > > +       u64 val;
> > > > +       int ret;
> > > > +
> > > > +       ret = pcc_chan_reg_read(&pchan->cmd_complete, &val);
> > > > +       if (ret)
> > > > +               return false;
> > > > +
> > > we indeed already check if cmd_complete register is exist.
> > > IMO, it can simply the code logic and reduce the risk of problems if we
> > > return true here for the type without this register.
> > > what do you think?
> > > 
> > IIUC, your concern is about returning true for type 4 when the register
> > doesn't exist, right ?
> Return true in advance for the type without the cmd_complete register.
> If support the register, we judge if the channel should respond the
> interrupt based on the value of cmd_complete, like bellow.

Right, sorry for missing that.

> 
> -->8
> +static bool pcc_mbox_cmd_complete_check(struct pcc_chan_info *pchan)
> +{
> +       u64 val;
> +       int ret;
> +
> +       ret = pcc_chan_reg_read(&pchan->cmd_complete, &val);
> +       if (ret)
> +               return false;
> +
> +        if (!pchan->cmd_complete.gas)
> +                return true;
> +

Yes we need the above check.

> +       /*
> +         * Judge if the channel respond the interrupt based on the value of
> +         * command complete.
> +         */
> +       val &= pchan->cmd_complete.status_mask;
> +       /*
> +        * If this is PCC slave subspace channel, then the command complete
> +        * bit 0 indicates that Platform is sending a notification and OSPM
> +        * needs to respond this interrupt to process this command.
> +        */
> +       if (pchan->type == ACPI_PCCT_TYPE_EXT_PCC_SLAVE_SUBSPACE)
> +               return !val;
> +       else
> +               return !!val;
> +}
> > I am saying it won't happen as we bail out if there is no GAS register
> > from pcc_chan_reg_init(). Or am I missing something here ?
> Yes, what you say is also ok. Just wondering if it is better to simply the
> logic.

Understood now.

> > > > +       val &= pchan->cmd_complete.status_mask;
> > > > +
> > > > +       /*
> > > > +        * If this is PCC slave subspace channel, then the command complete
> > > > +        * bit 0 indicates that Platform is sending a notification and OSPM
> > > > +        * needs to respond this interrupt to process this command.
> > > > +        */
> > > > +       if (pchan->type == ACPI_PCCT_TYPE_EXT_PCC_SLAVE_SUBSPACE)
> > > > +               return !val;
> > > > +       else
> > > > +               return !!val;
> > > This else branch is not applicable to type 3. type 3 will cannot respond
> > > interrupt.
> > Sorry I don't understand what you mean by that.
> Sorry for my mistake.
> I meant that the type2 channel always return false in this function and
> never respond the interrupt if no check for the GAS register.
> Because the 'val' for the type without the register is zero.
> >

Agreed as mentioned above, we need to bail out with true return if no GAS is
found.

--
Regards,
Sudeep