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

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Message-ID:
 <BL0PR04MB6564D0850FA21E845B558FAEFC4C2@BL0PR04MB6564.namprd04.prod.outlook.com>
Date: Tue, 22 Oct 2024 06:01:43 +0000
From: Avri Altman <Avri.Altman@....com>
To: Bart Van Assche <bvanassche@....org>, "Martin K . Petersen"
	<martin.petersen@...cle.com>
CC: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...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. I think I'll exclude this one from this series.
I want it to be clear that all instances are about removing redundant host_lock calls before register access.
Here, it’s a bit different since need to verify that the UFS interrupt handler is not active on another CPU.
I will follow your suggestion - but in another series.

Thanks,
Avri
> 
> Thanks,
> 
> Bart.