Re: [PATCH 4/6] mhi: pci_generic: No-Op for device_wake operations

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Mon, Mar 01, 2021 at 05:25:09PM +0100, Loic Poulain wrote:
> The wake_db register presence is highly speculative and can fuze MHI
> devices. Indeed, currently the wake_db register address is defined at
> entry 127 of the 'Channel doorbell array', thus writing to this address
> is equivalent to ringing the doorbell for channel 127, causing trouble
> with some device that get an unexpected channel 127 doorbell interrupt.
> 

what are those "some" devices?

> This change fixes that issue by setting wake get/put as no-op for
> pci_generic devices. The wake device sideband mechanism seems really
> specific to each device, and is AFAIK no defined by the MHI spec.
> 

s/no/not

> It also removes zeroing initialization of wake_db register during MMIO
> initialization, the register being set via wake_get/put accessors few
> cycles later during M0 transition.
> 

IIUC, the DEVICE_WAKE specified in the MHI spec corresponds to the wake doorbell
register. But in some cases, this rather happens to be a #WAKE sideband GPIO as
in PCIe.

> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> ---
>  drivers/bus/mhi/core/init.c   |  2 --
>  drivers/bus/mhi/pci_generic.c | 18 ++++++++++++++++++
>  2 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
> index 2159dbc..32eb90f 100644
> --- a/drivers/bus/mhi/core/init.c
> +++ b/drivers/bus/mhi/core/init.c
> @@ -510,8 +510,6 @@ int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
>  
>  	/* Setup wake db */
>  	mhi_cntrl->wake_db = base + val + (8 * MHI_DEV_WAKE_DB);
> -	mhi_write_reg(mhi_cntrl, mhi_cntrl->wake_db, 4, 0);
> -	mhi_write_reg(mhi_cntrl, mhi_cntrl->wake_db, 0, 0);

I need comment from Hemant/Bhaumik on this change since I don't exactly know if
this is really required or not.

Thanks,
Mani

>  	mhi_cntrl->wake_set = false;
>  
>  	/* Setup channel db address for each channel in tre_ring */
> diff --git a/drivers/bus/mhi/pci_generic.c b/drivers/bus/mhi/pci_generic.c
> index 87bab93..8423293 100644
> --- a/drivers/bus/mhi/pci_generic.c
> +++ b/drivers/bus/mhi/pci_generic.c
> @@ -312,6 +312,21 @@ static void mhi_pci_status_cb(struct mhi_controller *mhi_cntrl,
>  	}
>  }
>  
> +static void mhi_pci_wake_get_nop(struct mhi_controller *mhi_cntrl, bool force)
> +{
> +	/* no-op */
> +}
> +
> +static void mhi_pci_wake_put_nop(struct mhi_controller *mhi_cntrl, bool override)
> +{
> +	/* no-op */
> +}
> +
> +static void mhi_pci_wake_toggle_nop(struct mhi_controller *mhi_cntrl)
> +{
> +	/* no-op */
> +}
> +
>  static bool mhi_pci_is_alive(struct mhi_controller *mhi_cntrl)
>  {
>  	struct pci_dev *pdev = to_pci_dev(mhi_cntrl->cntrl_dev);
> @@ -515,6 +530,9 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	mhi_cntrl->status_cb = mhi_pci_status_cb;
>  	mhi_cntrl->runtime_get = mhi_pci_runtime_get;
>  	mhi_cntrl->runtime_put = mhi_pci_runtime_put;
> +	mhi_cntrl->wake_get = mhi_pci_wake_get_nop;
> +	mhi_cntrl->wake_put = mhi_pci_wake_put_nop;
> +	mhi_cntrl->wake_toggle = mhi_pci_wake_toggle_nop;
>  
>  	err = mhi_pci_claim(mhi_cntrl, info->bar_num, DMA_BIT_MASK(info->dma_data_width));
>  	if (err)
> -- 
> 2.7.4
>