linux-kernel - Re: [PATCH] scsi: ufs: ufshcd: Read device property for ref clock

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Date:   Fri, 15 Jul 2022 14:24:47 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Daniil Lunev <dlunev@...omium.org>,
        Bart Van Assche <bvanassche@....org>
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Bean Huo <beanhuo@...ron.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Jonathan Corbet <corbet@....net>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org
Subject: Re: [PATCH] scsi: ufs: ufshcd: Read device property for ref clock

On 15/07/22 14:03, Daniil Lunev wrote:
> UFS storage devices require bRefClkFreq attribute to be set to operate
> correctly at high speed mode. The necessary value is determined by what the
> SoC / board supports. The standard doesn't specify a method to query the
> value, so the information needs to be fed in separately.
> 
> DT information feeds into setting up the clock framework, so platforms
> using DT can get the UFS reference clock frequency from the clock
> framework. A special node "ref_clk" from the clock array for the UFS
> controller node is used as the source for the information.
> 
> On the platforms that do not use DT (e.g. Intel), the alternative mechanism
> to feed the intended reference clock frequency is necessary. Specifying the
> necessary information in DSD of the UFS controller ACPI node is an
> alternative mechanism proposed in this patch. Those can be accessed via
> firmware property facility in the kernel and in many ways simillar to
> querying properties defined in DT.
> 
> This patch introduces a small helper function to query a predetermined ACPI
> supplied property of the UFS controller, and uses it to attempt retrieving
> reference clock value, unless that was already done by the clock
> infrastructure.
> 
> Signed-off-by: Daniil Lunev <dlunev@...omium.org>

Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>

> 
> ---
> 
>  Documentation/scsi/ufs.rst | 15 +++++++++++++++
>  drivers/ufs/core/ufshcd.c  | 16 ++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/Documentation/scsi/ufs.rst b/Documentation/scsi/ufs.rst
> index fbac745b783ce..885b1a736e3f3 100644
> --- a/Documentation/scsi/ufs.rst
> +++ b/Documentation/scsi/ufs.rst
> @@ -17,6 +17,8 @@ Universal Flash Storage
>       3.2 UTP Transfer requests
>       3.3 UFS error handling
>       3.4 SCSI Error handling
> +   4. BSG Support
> +   5. UFS Reference Clock Frequency configuration
>  
>  
>  1. Overview
> @@ -193,3 +195,16 @@ UFS specifications can be found at:
>  
>  - UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
>  - UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf
> +
> +5. UFS Reference Clock Frequency configuration
> +==============================================
> +
> +Devicetree can define a clock named "ref_clk" under the UFS controller node
> +to specify the intended reference clock frequency for the UFS storage
> +parts. ACPI-based system can specify the frequency using ACPI
> +Device-Specific Data property named "ref-clk-freq". In both ways the value
> +is interpreted as frequency in Hz and must match one of the values given in
> +the UFS specification. UFS subsystem will attempt to read the value when
> +executing common controller initialization. If the value is available, UFS
> +subsytem will ensure the bRefClkFreq attribute of the UFS storage device is
> +set accordingly and will modify it if there is a mismatch.
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index ce86d1b790c05..78242f189f636 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -8536,6 +8536,19 @@ static int ufshcd_setup_clocks(struct ufs_hba *hba, bool on)
>  	return ret;
>  }
>  
> +static enum ufs_ref_clk_freq ufshcd_parse_ref_clk_property(struct ufs_hba *hba)
> +{
> +	u32 freq;
> +	int ret = device_property_read_u32(hba->dev, "ref-clk-freq", &freq);
> +
> +	if (ret) {
> +		dev_dbg(hba->dev, "Cannnot query 'ref-clk-freq' property = %d", ret);
> +		return REF_CLK_FREQ_INVAL;
> +	}
> +
> +	return ufs_get_bref_clk_from_hz(freq);
> +}
> +
>  static int ufshcd_init_clocks(struct ufs_hba *hba)
>  {
>  	int ret = 0;
> @@ -8629,6 +8642,9 @@ static int ufshcd_hba_init(struct ufs_hba *hba)
>  	if (err)
>  		goto out_disable_hba_vreg;
>  
> +	if (hba->dev_ref_clk_freq == REF_CLK_FREQ_INVAL)
> +		hba->dev_ref_clk_freq = ufshcd_parse_ref_clk_property(hba);
> +
>  	err = ufshcd_setup_clocks(hba, true);
>  	if (err)
>  		goto out_disable_hba_vreg;