linux-kernel - Re: [PATCH v4 3/9] PCI: epf-mhi: Add support for handling D-state notify from EPC

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Message-ID: <20230801172142.GA76659@thinkpad>
Date:   Tue, 1 Aug 2023 22:51:42 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc:     manivannan.sadhasivam@...aro.org, helgaas@...nel.org,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, quic_vbadigan@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_ramkri@...cinc.com, krzysztof.kozlowski@...aro.org,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        "open list:MHI BUS" <mhi@...ts.linux.dev>
Subject: Re: [PATCH v4 3/9] PCI: epf-mhi: Add support for handling D-state
 notify from EPC

On Tue, Aug 01, 2023 at 10:31:42AM +0530, Krishna Chaitanya Chundru wrote:
> 
> On 7/31/2023 11:05 AM, Krishna Chaitanya Chundru wrote:
> > 
> > On 7/28/2023 9:39 AM, Manivannan Sadhasivam wrote:
> > > On Thu, Jul 13, 2023 at 12:40:12PM +0530, Krishna chaitanya chundru
> > > wrote:
> > > > Add support for handling D-state notify for MHI EPF.
> > > > 
> > > > Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> > > > ---
> > > >   drivers/pci/endpoint/functions/pci-epf-mhi.c | 11 +++++++++++
> > > >   include/linux/mhi_ep.h                       |  3 +++
> > > >   2 files changed, 14 insertions(+)
> > > > 
> > > > diff --git a/drivers/pci/endpoint/functions/pci-epf-mhi.c
> > > > b/drivers/pci/endpoint/functions/pci-epf-mhi.c
> > > > index 9c1f5a1..ee91bfc 100644
> > > > --- a/drivers/pci/endpoint/functions/pci-epf-mhi.c
> > > > +++ b/drivers/pci/endpoint/functions/pci-epf-mhi.c
> > > > @@ -339,6 +339,16 @@ static int pci_epf_mhi_bme(struct pci_epf *epf)
> > > >       return 0;
> > > >   }
> > > >   +static int pci_epf_mhi_dstate_notify(struct pci_epf *epf,
> > > > pci_power_t state)
> > > > +{
> > > > +    struct pci_epf_mhi *epf_mhi = epf_get_drvdata(epf);
> > > > +    struct mhi_ep_cntrl *mhi_cntrl = &epf_mhi->mhi_cntrl;
> > > > +
> > > > +    mhi_cntrl->dstate = state;
> > > Where is this variable being used? Also, don't we need any locking?
> > > 
> > > - Mani
> > 
> > we are using this variable in wakeup host op which is introduced on
> > patch [PATCH v4 8/9] PCI: epf-mhi: Add wakeup host op
> > 
> > I will add lock in my next series.
> > 
> > - KC
> 
> Mani, as this is being called from IRQ context do we need to add any lock
> here.
> 

Notifiers are invoked in process context. And here, the context doesn't matter
as either way you need locking to prevent concurrent access to dstate variable.

But I think it is safe to ignore lock for now provided that wakeup_host callback
is only called while MHI is in M3 state. Even if dstate changes while processing
wakeup_host, it won't affect the behavior.

- Mani

> - KC
> 
> > 
> > > 
> > > > +
> > > > +    return 0;
> > > > +}
> > > > +
> > > >   static int pci_epf_mhi_bind(struct pci_epf *epf)
> > > >   {
> > > >       struct pci_epf_mhi *epf_mhi = epf_get_drvdata(epf);
> > > > @@ -394,6 +404,7 @@ static struct pci_epc_event_ops
> > > > pci_epf_mhi_event_ops = {
> > > >       .link_up = pci_epf_mhi_link_up,
> > > >       .link_down = pci_epf_mhi_link_down,
> > > >       .bme = pci_epf_mhi_bme,
> > > > +    .dstate_notify = pci_epf_mhi_dstate_notify,
> > > >   };
> > > >     static int pci_epf_mhi_probe(struct pci_epf *epf,
> > > > diff --git a/include/linux/mhi_ep.h b/include/linux/mhi_ep.h
> > > > index f198a8a..c3a0685 100644
> > > > --- a/include/linux/mhi_ep.h
> > > > +++ b/include/linux/mhi_ep.h
> > > > @@ -8,6 +8,7 @@
> > > >     #include <linux/dma-direction.h>
> > > >   #include <linux/mhi.h>
> > > > +#include <linux/pci.h>
> > > >     #define MHI_EP_DEFAULT_MTU 0x8000
> > > >   @@ -139,6 +140,8 @@ struct mhi_ep_cntrl {
> > > >         enum mhi_state mhi_state;
> > > >   +    pci_power_t dstate;
> > > > +
> > > >       u32 max_chan;
> > > >       u32 mru;
> > > >       u32 event_rings;
> > > > -- 
> > > > 2.7.4
> > > > 
> > 

-- 
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