Re: [PATCH] mhi: pci_generic: Ensure device readiness before starting MHI

[Jeffrey Hugo <jhugo@codeaurora.org>]

On 2/11/2021 10:08 AM, Loic Poulain wrote:
> The PCI device may have not been bound from cold boot and be in
> undefined state, or simply not yet ready for MHI operations. This
> change ensures that the MHI layer is reset to initial state and
> ready for MHI initialization and power up.
> 
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> ---
>   drivers/bus/mhi/pci_generic.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/bus/mhi/pci_generic.c b/drivers/bus/mhi/pci_generic.c
> index c20f59e..bfa0a1e 100644
> --- a/drivers/bus/mhi/pci_generic.c
> +++ b/drivers/bus/mhi/pci_generic.c
> @@ -17,6 +17,8 @@
>   #include <linux/timer.h>
>   #include <linux/workqueue.h>
>   
> +#include "core/internal.h"
> +
>   #define MHI_PCI_DEFAULT_BAR_NUM 0
>   
>   #define MHI_POST_RESET_DELAY_MS 500
> @@ -391,6 +393,22 @@ static void health_check(struct timer_list *t)
>   	mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
>   }
>   
> +static void __mhi_sw_reset(struct mhi_controller *mhi_cntrl)
> +{
> +	unsigned int max_wait_ready = 200;
> +
> +	mhi_pci_write_reg(mhi_cntrl, mhi_cntrl->regs + MHICTRL,
> +			  MHICTRL_RESET_MASK);
> +
> +	while (mhi_get_mhi_state(mhi_cntrl) != MHI_STATE_READY) {
> +		if (!max_wait_ready--) {
> +			dev_warn(mhi_cntrl->cntrl_dev, "Not ready\n");
> +			break;
> +		}
> +		msleep(50);
> +	}
> +}
> +
>   static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>   {
>   	const struct mhi_pci_dev_info *info = (struct mhi_pci_dev_info *) id->driver_data;
> @@ -451,6 +469,9 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>   		goto err_unregister;
>   	}
>   
> +	/* Before starting MHI, ensure device is in good initial state */
> +	__mhi_sw_reset(mhi_cntrl);
> +
>   	err = mhi_sync_power_up(mhi_cntrl);
>   	if (err) {
>   		dev_err(&pdev->dev, "failed to power up MHI controller\n");
> @@ -532,6 +553,8 @@ static void mhi_pci_reset_done(struct pci_dev *pdev)
>   		return;
>   	}
>   
> +	__mhi_sw_reset(mhi_cntrl);
> +
>   	err = mhi_sync_power_up(mhi_cntrl);
>   	if (err) {
>   		dev_err(&pdev->dev, "failed to power up MHI controller\n");
> 

So, I'm curious, how does this actually work?

 From what I can see, you define SBL images.  If those get loaded by the 
PBL, it doesn't happen over MHI.  PBL will not move MHI to ready state, 
except in the specific instance of a fatal error.

Your above change works if the device comes up straight in mission mode 
(AMSS), but if it comes up in PBL, you are going to hit the timeout and 
dev_warn() every time.

-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.