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

[Dmitry Baryshkov]

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@xxxxxxxxxx>
> > > ---
> > >    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