From: Can Guo <cang@codeaurora.org>
To: Stanley Chu <stanley.chu@mediatek.com>
Cc: linux-scsi@vger.kernel.org, martin.petersen@oracle.com,
avri.altman@wdc.com, alim.akhtar@samsung.com, jejb@linux.ibm.com,
bvanassche@acm.org, beanhuo@micron.com, asutoshd@codeaurora.org,
matthias.bgg@gmail.com, linux-mediatek@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, kuohong.wang@mediatek.com,
peter.wang@mediatek.com, chun-hung.wu@mediatek.com,
andy.teng@mediatek.com, chaotian.jing@mediatek.com,
cc.chou@mediatek.com
Subject: Re: [PATCH v2] scsi: ufs: Fix possible infinite loop in ufshcd_hold
Date: Wed, 29 Jul 2020 16:43:27 +0800 [thread overview]
Message-ID: <bfbb48b06fa3464da0cbd2aee8a32649@codeaurora.org> (raw)
In-Reply-To: <20200729024037.23105-1-stanley.chu@mediatek.com>
Hi Stanley,
On 2020-07-29 10:40, Stanley Chu wrote:
> In ufshcd_suspend(), after clk-gating is suspended and link is set
> as Hibern8 state, ufshcd_hold() is still possibly invoked before
> ufshcd_suspend() returns. For example, MediaTek's suspend vops may
> issue UIC commands which would call ufshcd_hold() during the command
> issuing flow.
>
> Now if UFSHCD_CAP_HIBERN8_WITH_CLK_GATING capability is enabled,
> then ufshcd_hold() may enter infinite loops because there is no
> clk-ungating work scheduled or pending. In this case, ufshcd_hold()
> shall just bypass, and keep the link as Hibern8 state.
>
The infinite loop is expected as ufshcd_hold is called again after
link is put to hibern8 state, so in QCOM's code, we never do this.
The cap UFSHCD_CAP_HIBERN8_WITH_CLK_GATING means UIC link state
must not be HIBERN8 after ufshcd_hold(async=false) returns.
Instead of bailing out from that loop, which makes the logic of
ufshcd_hold and clk gating even more complex, how about removing
ufshcd_hold/release from ufshcd_send_uic_cmd()? I think they are
redundant and we should never send DME cmds if clocks/powers are
not ready. I mean callers should make sure they are ready to send
DME cmds (and only callers know when), but not leave that job to
ufshcd_send_uic_cmd(). It is convenient to remove ufshcd_hold/
release from ufshcd_send_uic_cmd() as there are not many places
sending DME cmds without holding the clocks, ufs_bsg.c is one.
And I have tested my idea on my setup, it worked well for me.
Another benefit is that it also allows us to use DME cmds
in clk gating/ungating contexts if we need to in the future.
Please let me know your idea, thanks.
Can Guo.
> Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
> Signed-off-by: Andy Teng <andy.teng@mediatek.com>
>
> ---
>
> Changes since v1:
> - Fix return value: Use unique bool variable to get the result of
> flush_work(). Thcan prevent incorrect returned value, i.e., rc, if
> flush_work() returns true
> - Fix commit message
>
> ---
> drivers/scsi/ufs/ufshcd.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 577cc0d7487f..acba2271c5d3 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1561,6 +1561,7 @@ static void ufshcd_ungate_work(struct work_struct
> *work)
> int ufshcd_hold(struct ufs_hba *hba, bool async)
> {
> int rc = 0;
> + bool flush_result;
> unsigned long flags;
>
> if (!ufshcd_is_clkgating_allowed(hba))
> @@ -1592,7 +1593,9 @@ int ufshcd_hold(struct ufs_hba *hba, bool async)
> break;
> }
> spin_unlock_irqrestore(hba->host->host_lock, flags);
> - flush_work(&hba->clk_gating.ungate_work);
> + flush_result = flush_work(&hba->clk_gating.ungate_work);
> + if (hba->clk_gating.is_suspended && !flush_result)
> + goto out;
> spin_lock_irqsave(hba->host->host_lock, flags);
> goto start;
> }
next prev parent reply other threads:[~2020-07-29 8:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-29 2:40 [PATCH v2] scsi: ufs: Fix possible infinite loop in ufshcd_hold Stanley Chu
2020-07-29 8:43 ` Can Guo [this message]
2020-07-29 10:26 ` Stanley Chu
2020-07-29 10:53 ` Can Guo
2020-07-30 7:59 ` Stanley Chu
[not found] ` <1596518850.27829.5.camel@mtkswgap22>
[not found] ` <BYAPR04MB4629D947CAC7E07FF94D55F2FC4A0@BYAPR04MB4629.namprd04.prod.outlook.com>
2020-08-07 0:39 ` Stanley Chu
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