linux-kernel - Re: [PATCH 4/4] scsi: ufs: core: Use reg

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Message-ID: <c58e4fce-0a74-4469-ad16-f1edbd670728@acm.org>
Date: Mon, 21 Oct 2024 13:02:59 -0700
From: Bart Van Assche <bvanassche@....org>
To: Avri Altman <avri.altman@....com>,
 "Martin K . Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] scsi: ufs: core: Use reg_lock to protect HCE register

On 10/21/24 5:03 AM, Avri Altman wrote:
> Use the host register lock to serialize access to the Host Controller
> Enable (HCE) register as well, instead of the host_lock.
> 
> Signed-off-by: Avri Altman <avri.altman@....com>
> ---
>   drivers/ufs/core/ufshcd.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 4eee737a4fd5..3cc8ffc6929f 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -4795,9 +4795,9 @@ void ufshcd_hba_stop(struct ufs_hba *hba)
>   	 * Obtain the host lock to prevent that the controller is disabled
>   	 * while the UFS interrupt handler is active on another CPU.
>   	 */
> -	spin_lock_irqsave(hba->host->host_lock, flags);
> +	spin_lock_irqsave(&hba->reg_lock, flags);
>   	ufshcd_writel(hba, CONTROLLER_DISABLE,  REG_CONTROLLER_ENABLE);
> -	spin_unlock_irqrestore(hba->host->host_lock, flags);
> +	spin_unlock_irqrestore(&hba->reg_lock, flags);
>   
>   	err = ufshcd_wait_for_register(hba, REG_CONTROLLER_ENABLE,
>   					CONTROLLER_ENABLE, CONTROLLER_DISABLE,

Hi Avri,

How about proceeding as follows for ufshcd_hba_stop():
* Remove the comment above the ufshcd_writel() call and add a
   disable_irq() call instead.
* Call enable_irq() after ufshcd_writel() has finished and before
   ufshcd_wait_for_register() is called.
* Do not hold any lock around the ufshcd_writel() call.

Although the legacy interrupt is disabled by some but not all
ufshcd_hba_stop() callers, I think it is safe to nest disable_irq()
calls. From kernel/irq/manage.c:

void __disable_irq(struct irq_desc *desc)
{
	if (!desc->depth++)
		irq_disable(desc);
}

Thanks,

Bart.