linux-kernel - Re: [PATCH] bus: mhi: host: pci: Disable runtime PM for QDU100

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Message-ID: <tbktzaxkgsc6d4ma4o6vkkcpnqiwghxkvwryrm36znepgqjotl@5n3di2ew3s6f>
Date: Fri, 18 Apr 2025 18:15:45 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Vivek Pernamitta <quic_vpernami@...cinc.com>
Cc: Veerabhadrarao Badiganti <quic_vbadigan@...cinc.com>, 
	mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bus: mhi: host: pci: Disable runtime PM for QDU100

On Fri, Apr 18, 2025 at 03:40:48PM +0530, Vivek Pernamitta wrote:
> 
> 
> On 4/18/2025 3:04 PM, Vivek Pernamitta wrote:
> > 
> > 
> > On 4/18/2025 2:06 PM, Manivannan Sadhasivam wrote:
> > > On Fri, Apr 18, 2025 at 11:55:24AM +0530, Vivek Pernamitta wrote:
> > > > 
> > > > 
> > > > On 4/17/2025 11:37 AM, Manivannan Sadhasivam wrote:
> > > > > On Thu, Apr 17, 2025 at 10:00:38AM +0530, Veerabhadrarao
> > > > > Badiganti wrote:
> > > > > > 
> > > > > > On 4/14/2025 1:17 PM, Vivek Pernamitta wrote:
> > > > > > > The QDU100 device does not support the MHI M3 state,
> > > > > > > necessitating the
> > > > > > > disabling of runtime PM for this device. Since the
> > > > > > > PCIe core framework
> > > > > > > enables runtime PM by default for all clients, it is
> > > > > > > essential to disable
> > > > > > > runtime PM if the device does not support Low Power Mode (LPM).
> > > > > > > 
> > > 
> > > Not true... See below.
> > > 
> > > > > > > Signed-off-by: Vivek Pernamitta<quic_vpernami@...cinc.com>
> > > > > > > ---
> > > > > > >     drivers/bus/mhi/host/pci_generic.c | 10 ++++++++++
> > > > > > >     1 file changed, 10 insertions(+)
> > > > > > > 
> > > > > > > diff --git a/drivers/bus/mhi/host/pci_generic.c
> > > > > > > b/drivers/bus/mhi/ host/pci_generic.c
> > > > > > > index 03aa887952098661a488650053a357f883d1559b..a011fd2d48c57cf9d1aec74040153267a206d797
> > > > > > > 100644
> > > > > > > --- a/drivers/bus/mhi/host/pci_generic.c
> > > > > > > +++ b/drivers/bus/mhi/host/pci_generic.c
> > > > > > > @@ -43,6 +43,7 @@
> > > > > > >      * @mru_default: default MRU size for MBIM network packets
> > > > > > >      * @sideband_wake: Devices using dedicated
> > > > > > > sideband GPIO for wakeup instead
> > > > > > >      *           of inband wake support (such as sdx24)
> > > > > > > + * @pm_disable: disables runtime PM (optional)
> > > > > > >      */
> > > > > > >     struct mhi_pci_dev_info {
> > > > > > >         const struct mhi_controller_config *config;
> > > > > > > @@ -54,6 +55,7 @@ struct mhi_pci_dev_info {
> > > > > > >         unsigned int dma_data_width;
> > > > > > >         unsigned int mru_default;
> > > > > > >         bool sideband_wake;
> > > > > > > +    bool pm_disable;
> > > > > > >     };
> > > > > > >     #define MHI_CHANNEL_CONFIG_UL(ch_num, ch_name,
> > > > > > > el_count, ev_ring) \
> > > > > > > @@ -295,6 +297,7 @@ static const struct
> > > > > > > mhi_pci_dev_info mhi_qcom_qdu100_info = {
> > > > > > >         .bar_num = MHI_PCI_DEFAULT_BAR_NUM,
> > > > > > >         .dma_data_width = 32,
> > > > > > >         .sideband_wake = false,
> > > > > > > +    .pm_disable = true,
> > > > > > 
> > > > > > |no_m3|orno_|m3_support|would be more suitable than|pm_disable|
> > > > > 
> > > > > Yes!
> > > > > 
> We named variable pm_disable because the M3 state is implicitly set during
> runtime PM suspend. Both are not needed and not fully supported for the
> QDU100 accelerator card, so we want to disable runtime suspend for it.

You are mixing terms here. Only M3 is not supported by the device. The fact that
you do not want to enable runtime PM for the device to avoid latency is a side
effect of that. So you need to name the variable as 'no_m3'.

- Mani

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