linux-kernel - Re: [PATCH 1/3] ufs: ufs-qcom: Add support for DT-based gear and rate limiting

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Message-ID: <f61ac7b6-5e63-49cb-b051-a749037e0c8b@quicinc.com>
Date: Thu, 24 Jul 2025 13:05:21 +0530
From: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
CC: <mani@...nel.org>, <alim.akhtar@...sung.com>, <avri.altman@....com>,
        <bvanassche@....org>, <robh@...nel.org>, <krzk+dt@...nel.org>,
        <conor+dt@...nel.org>, <andersson@...nel.org>,
        <konradybcio@...nel.org>, <James.Bottomley@...senpartnership.com>,
        <martin.petersen@...cle.com>, <agross@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] ufs: ufs-qcom: Add support for DT-based gear and rate
 limiting



On 23-Jul-25 12:24 AM, Dmitry Baryshkov wrote:
> On Tue, Jul 22, 2025 at 09:41:01PM +0530, Ram Kumar Dwivedi wrote:
>> Add optional device tree properties to limit Tx/Rx gear and rate during UFS
>> initialization. Parse these properties in ufs_qcom_init() and apply them to
>> host->host_params to enforce platform-specific constraints.
>>
>> Use this mechanism to cap the maximum gear or rate on platforms with
>> hardware limitations, such as those required by some automotive customers
>> using SA8155. Preserve the default behavior if the properties are not
>> specified in the device tree.
>>
>> Signed-off-by: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
>> ---
>>  drivers/ufs/host/ufs-qcom.c | 28 ++++++++++++++++++++++------
>>  1 file changed, 22 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
>> index 4bbe4de1679b..5e7fd3257aca 100644
>> --- a/drivers/ufs/host/ufs-qcom.c
>> +++ b/drivers/ufs/host/ufs-qcom.c
>> @@ -494,12 +494,8 @@ static int ufs_qcom_power_up_sequence(struct ufs_hba *hba)
>>  	 * If the HS-G5 PHY gear is used, update host_params->hs_rate to Rate-A,
>>  	 * so that the subsequent power mode change shall stick to Rate-A.
>>  	 */
>> -	if (host->hw_ver.major == 0x5) {
>> -		if (host->phy_gear == UFS_HS_G5)
>> -			host_params->hs_rate = PA_HS_MODE_A;
>> -		else
>> -			host_params->hs_rate = PA_HS_MODE_B;
>> -	}
>> +	if (host->hw_ver.major == 0x5 && host->phy_gear == UFS_HS_G5)
>> +		host_params->hs_rate = PA_HS_MODE_A;
> 
> Why? This doesn't seem related.

Hi Dmitry,

I have refactored the patch to put this part in a separate patch in latest patchset.

Thanks,
Ram.

> 
>>  
>>  	mode = host_params->hs_rate == PA_HS_MODE_B ? PHY_MODE_UFS_HS_B : PHY_MODE_UFS_HS_A;
>>  
>> @@ -1096,6 +1092,25 @@ static void ufs_qcom_set_phy_gear(struct ufs_qcom_host *host)
>>  	}
>>  }
>>  
>> +static void ufs_qcom_parse_limits(struct ufs_qcom_host *host)
>> +{
>> +	struct ufs_host_params *host_params = &host->host_params;
>> +	struct device_node *np = host->hba->dev->of_node;
>> +	u32 hs_gear, hs_rate = 0;
>> +
>> +	if (!np)
>> +		return;
>> +
>> +	if (!of_property_read_u32(np, "limit-hs-gear", &hs_gear)) {
> 
> These are generic properties, so they need to be handled in a generic
> code path.

Hi Dmitry,


Below is the probe path for the UFS-QCOM platform driver:

ufs_qcom_probe
  └─ ufshcd_platform_init
       └─ ufshcd_init
            └─ ufs_qcom_init
                 └─ ufs_qcom_set_host_params
                      └─ ufshcd_init_host_params (initialized with default values)
                           └─ ufs_qcom_get_hs_gear (overrides gear based on controller capability)
                                └─ ufs_qcom_set_phy_gear (further overrides based on controller limitations)


The reason I added the logic in ufs-qcom.c is that even if it's placed in ufshcd-platform.c, the values get overridden in ufs-qcom.c.
If you prefer, I can move the parsing logic API to ufshcd-platform.c but still it needs to be called from ufs-qcom.c.

Thanks,
Ram.


> 
> Also, the patch with bindings should preceed driver and DT changes.

Hi Dmitry,

I have reordered the patch series to place the DT binding change as the first patch in latest patchset.

Thanks,
Ram.


> 
>> +		host_params->hs_tx_gear = hs_gear;
>> +		host_params->hs_rx_gear = hs_gear;
>> +		host->phy_gear = hs_gear;
>> +	}
>> +
>> +	if (!of_property_read_u32(np, "limit-rate", &hs_rate))
>> +		host_params->hs_rate = hs_rate;
>> +}
>> +
>>  static void ufs_qcom_set_host_params(struct ufs_hba *hba)
>>  {
>>  	struct ufs_qcom_host *host = ufshcd_get_variant(hba);
>> @@ -1337,6 +1352,7 @@ static int ufs_qcom_init(struct ufs_hba *hba)
>>  	ufs_qcom_advertise_quirks(hba);
>>  	ufs_qcom_set_host_params(hba);
>>  	ufs_qcom_set_phy_gear(host);
>> +	ufs_qcom_parse_limits(host);
>>  
>>  	err = ufs_qcom_ice_init(host);
>>  	if (err)
>> -- 
>> 2.50.1
>>
>