Re: [PATCH V4 10/11] scsi: ufs: qcom : Introduce phy_power_on/off wrapper function

From: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
To: Nitin Rawat <quic_nitirawa@quicinc.com>,
	vkoul@kernel.org, kishon@kernel.org,
	manivannan.sadhasivam@linaro.org,
	James.Bottomley@HansenPartnership.com,
	martin.petersen@oracle.com, bvanassche@acm.org,
	andersson@kernel.org, neil.armstrong@linaro.org
Cc: quic_rdwivedi@quicinc.com, quic_cang@quicinc.com,
	linux-arm-msm@vger.kernel.org, linux-phy@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH V4 10/11] scsi: ufs: qcom : Introduce phy_power_on/off wrapper function
Date: Fri, 9 May 2025 14:00:48 +0200	[thread overview]
Message-ID: <4a72ea06-22a8-4f8c-92ad-b5b3afa25b70@oss.qualcomm.com> (raw)
In-Reply-To: <be69cd1e-c04c-4976-9be1-390631316d3f@quicinc.com>

On 5/9/25 1:49 PM, Nitin Rawat wrote:
> 
> 
> On 5/9/2025 5:07 PM, Konrad Dybcio wrote:
>> On 5/3/25 6:24 PM, Nitin Rawat wrote:
>>> Introduce ufs_qcom_phy_power_on and ufs_qcom_phy_power_off wrapper
>>> functions with mutex protection to ensure safe usage of is_phy_pwr_on
>>> and prevent possible race conditions.
>>>
>>> Co-developed-by: Can Guo <quic_cang@quicinc.com>
>>> Signed-off-by: Can Guo <quic_cang@quicinc.com>
>>> Signed-off-by: Nitin Rawat <quic_nitirawa@quicinc.com>
>>> ---
>>
>> The PHY framework does the same thing internally already, this seems
>> unnecessary
> 
> Hi Konrad,
> 
> Thanks for the review. There are scenarios where ufshcd_link_startup() can call ufshcd_vops_link_startup_notify() multiple times during retries. This leads to the PHY reference count increasing continuously, preventing proper re-initialization of the PHY.

I'm assuming you're talking about the scenario where it jumps into
ufs_qcom_power_up_sequence() - you have a label in there called
`out_disable_phy` - add a phy_power_off() after phy_calibrate if
things fail and you should be good to go if I'm reading things right.

Please include something resembling a call stack in the commit message,
as currently everyone reviewing this has to make guesses about why this
needs to be done

> Recently, this issue was addressed with patch 7bac65687510 ("scsi: ufs:
> qcom: Power off the PHY if it was already powered on in ufs_qcom_power_up_sequence()"). However, I still want to maintain a reference count (ref_cnt) to safeguard against similar conditions in the code. Additionally, this approach helps avoid unnecessary phy_power_on and phy_power_off calls. Please let me know your thoughts.

These unnecessary calls only amount to a couple of jumps and compares,
just like your wrappers, as the framework keeps track of the enable
count as well

Konrad

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