linux-kernel - Re: [PATCH 14/15] scsi: ufs: ufs-qcom: Add support for finding HS gear on new UFS versions

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Date:   Mon, 31 Oct 2022 21:52:36 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     martin.petersen@...cle.com, jejb@...ux.ibm.com,
        andersson@...nel.org, vkoul@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, konrad.dybcio@...ainline.org,
        robh+dt@...nel.org, quic_cang@...cinc.com,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-scsi@...r.kernel.org
Subject: Re: [PATCH 14/15] scsi: ufs: ufs-qcom: Add support for finding HS
 gear on new UFS versions

On 31/10/2022 17:56, Manivannan Sadhasivam wrote:
> On Sun, Oct 30, 2022 at 12:48:21AM +0300, Dmitry Baryshkov wrote:
>> On 29/10/2022 17:16, Manivannan Sadhasivam wrote:
>>> Starting from UFS controller v4, Qcom supports dual gear mode (i.e., the
>>> controller/PHY can be configured to run in two gear speeds). But that
>>> requires an agreement between the UFS controller and the UFS device.
>>> This commit finds the max gear supported by both controller and device
>>> then decides which one to use.
>>>
>>> UFS controller's max gear can be read from the REG_UFS_PARAM0 register and
>>> UFS device's max gear can be read from the "max-gear" devicetree property.
>>>
>>> The UFS PHY also needs to be configured with the decided gear using the
>>> phy_set_mode_ext() API.
>>>
>>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
>>> ---
>>>    drivers/ufs/host/ufs-qcom.c | 35 ++++++++++++++++++++++++++++++++---
>>>    drivers/ufs/host/ufs-qcom.h |  4 ++++
>>>    2 files changed, 36 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
>>> index f952cc76919f..268463e92d67 100644
>>> --- a/drivers/ufs/host/ufs-qcom.c
>>> +++ b/drivers/ufs/host/ufs-qcom.c
>>> @@ -281,6 +281,9 @@ static int ufs_qcom_host_reset(struct ufs_hba *hba)
>>>    static u32 ufs_qcom_get_hs_gear(struct ufs_hba *hba, u32 hs_gear)
>>>    {
>>>    	struct ufs_qcom_host *host = ufshcd_get_variant(hba);
>>> +	struct device *dev = hba->dev;
>>> +	u32 max_gear, hcd_max_gear, reg;
>>> +	int ret;
>>>    	if (host->hw_ver.major == 0x1) {
>>>    		/*
>>> @@ -292,8 +295,33 @@ static u32 ufs_qcom_get_hs_gear(struct ufs_hba *hba, u32 hs_gear)
>>>    		 */
>>>    		if (hs_gear > UFS_HS_G2)
>>>    			return UFS_HS_G2;
>>> +	} else if (host->hw_ver.major > 0x3) {
>>> +		/*
>>> +		 * Starting from UFS controller v4, Qcom supports dual gear mode (i.e., the
>>> +		 * controller/PHY can be configured to run in two gear speeds). But that
>>> +		 * requires an agreement between the UFS controller and the device. Below
>>> +		 * code tries to find the max gear of both and decides which gear to use.
>>> +		 *
>>> +		 * First get the max gear supported by the UFS device if available.
>>> +		 * If the property is not defined in devicetree, then use the default gear.
>>> +		 */
>>> +		ret = of_property_read_u32(dev->of_node, "max-gear", &max_gear);
>>> +		if (ret)
>>> +			goto err_out;
>>
>> Can we detect the UFS device's max gear somehow? If not, the 'max-gear'
>> property name doesn't sound good. Maybe calling it 'device-gear' would be
>> better.
>>
> 
> UFS device probing depends on PHY init sequence. So technically we cannot know
> the max gear of the device without using an init sequence, but this information
> is static and should be known to a board manufacturer. That's why I decided to
> use this property. Another option is to use a fixed init sequence for probing
> the device and do a re-init after knowing it's max gear but that is not
> recommended.
> 
> We need "max" keyword because this property specifies the maximum gear at which
> the device could operate and not necessarily the gear at which it operates.
> Maybe, "max-device-gear" would make it clear.

Ack, thank you for the explanation. Yes, from my opinion max-device-gear 
is better. Let's see what Rob and Krzysztof would say.


-- 
With best wishes
Dmitry