netdev - Re: [PATCH net-next] bnxt_en: add unlocked version of bnxt_refclk

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Message-ID: <CALs4sv1VTT7L9t+BjuvW8naO7fm5Wq0qKgVkv2DW4nrNe1bucA@mail.gmail.com>
Date: Thu, 7 Nov 2024 10:00:14 +0530
From: Pavan Chebbi <pavan.chebbi@...adcom.com>
To: Vadim Fedorenko <vadfed@...a.com>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, Michael Chan <michael.chan@...adcom.com>, 
	Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>, Paolo Abeni <pabeni@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org, 
	Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH net-next] bnxt_en: add unlocked version of bnxt_refclk_read

On Thu, Nov 7, 2024 at 3:02 AM Vadim Fedorenko <vadfed@...a.com> wrote:
>
> Serialization of PHC read with FW reset mechanism uses ptp_lock which
> also protects timecounter updates. This means we cannot grab it when
> called from bnxt_cc_read(). Let's move locking into different function.
>
> Fixes: 6c0828d00f07 ("bnxt_en: replace PTP spinlock with seqlock")
> Signed-off-by: Vadim Fedorenko <vadfed@...a.com>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c | 29 ++++++++++++-------
>  1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
> index f74afdab4f7d..5395f125b601 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
> @@ -73,19 +73,15 @@ static int bnxt_ptp_settime(struct ptp_clock_info *ptp_info,
>         return 0;
>  }
>
> -static int bnxt_refclk_read(struct bnxt *bp, struct ptp_system_timestamp *sts,
> -                           u64 *ns)
> +/* Caller holds ptp_lock */
> +static int __bnxt_refclk_read(struct bnxt *bp, struct ptp_system_timestamp *sts,
> +                             u64 *ns)
>  {
>         struct bnxt_ptp_cfg *ptp = bp->ptp_cfg;
>         u32 high_before, high_now, low;
> -       unsigned long flags;
>
> -       /* We have to serialize reg access and FW reset */
> -       read_seqlock_excl_irqsave(&ptp->ptp_lock, flags);
> -       if (test_bit(BNXT_STATE_IN_FW_RESET, &bp->state)) {
> -               read_sequnlock_excl_irqrestore(&ptp->ptp_lock, flags);
> +       if (test_bit(BNXT_STATE_IN_FW_RESET, &bp->state))
>                 return -EIO;
> -       }
>
>         high_before = readl(bp->bar0 + ptp->refclk_mapped_regs[1]);
>         ptp_read_system_prets(sts);
> @@ -97,12 +93,25 @@ static int bnxt_refclk_read(struct bnxt *bp, struct ptp_system_timestamp *sts,
>                 low = readl(bp->bar0 + ptp->refclk_mapped_regs[0]);
>                 ptp_read_system_postts(sts);
>         }
> -       read_sequnlock_excl_irqrestore(&ptp->ptp_lock, flags);
>         *ns = ((u64)high_now << 32) | low;
>
>         return 0;
>  }
>
> +static int bnxt_refclk_read(struct bnxt *bp, struct ptp_system_timestamp *sts,
> +                           u64 *ns)
> +{
> +       struct bnxt_ptp_cfg *ptp = bp->ptp_cfg;
> +       unsigned long flags;
> +       int rc;
> +
> +       /* We have to serialize reg access and FW reset */
> +       read_seqlock_excl_irqsave(&ptp->ptp_lock, flags);
> +       rc = __bnxt_refclk_read(bp, sts, ns);
> +       read_sequnlock_excl_irqrestore(&ptp->ptp_lock, flags);
> +       return rc;
> +}
> +
>  static void bnxt_ptp_get_current_time(struct bnxt *bp)
>  {
>         struct bnxt_ptp_cfg *ptp = bp->ptp_cfg;
> @@ -674,7 +683,7 @@ static u64 bnxt_cc_read(const struct cyclecounter *cc)
>         struct bnxt_ptp_cfg *ptp = container_of(cc, struct bnxt_ptp_cfg, cc);
>         u64 ns = 0;
>
> -       bnxt_refclk_read(ptp->bp, NULL, &ns);
> +       __bnxt_refclk_read(ptp->bp, NULL, &ns);

With this change, bnxt_cc_read() is executed without protection during
timecounter_init(), right?
I think we should hold the ptp_lock inside bnxt_ptp_timecounter_init()
just like we do in bnxt_ptp_init_rtc()

>         return ns;
>  }
>
> --
> 2.43.5
>

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