scsi: ufs: core: Allow host driver to disable wb toggling during clock scaling

Mediatek UFS does not want to toggle write booster during clock scaling.
Permit host driver to disable wb toggling during clock scaling.

Introduce a flag UFSHCD_CAP_WB_WITH_CLK_SCALING to decouple WB and clock
scaling. UFSHCD_CAP_WB_WITH_CLK_SCALING is only valid when
UFSHCD_CAP_CLK_SCALING is set. Just like UFSHCD_CAP_HIBERN8_WITH_CLK_GATING
is valid only when UFSHCD_CAP_CLK_GATING set.

Set UFSHCD_CAP_WB_WITH_CLK_SCALING for qcom to compatible legacy design at
the same time.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Stanley Chu <[e-mail]>
Signed-off-by: Peter Wang <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/ufs/core/ufs-sysfs.c

···
 	unsigned int wb_enable;
 	ssize_t res;
 
-	if (!ufshcd_is_wb_allowed(hba) || ufshcd_is_clkscaling_supported(hba)) {
+	if (!ufshcd_is_wb_allowed(hba) || (ufshcd_is_clkscaling_supported(hba)
+		&& ufshcd_enable_wb_if_scaling_up(hba))) {
 		/*
 		 * If the platform supports UFSHCD_CAP_CLK_SCALING, turn WB
 		 * on/off will be done while clock scaling up/down.

drivers/ufs/core/ufshcd.c

···
 	}
 
 	/* Enable Write Booster if we have scaled up else disable it */
-	downgrade_write(&hba->clk_scaling_lock);
-	is_writelock = false;
-	ufshcd_wb_toggle(hba, scale_up);
+	if (ufshcd_enable_wb_if_scaling_up(hba)) {
+		downgrade_write(&hba->clk_scaling_lock);
+		is_writelock = false;
+		ufshcd_wb_toggle(hba, scale_up);
+	}
 
 out_unprepare:
 	ufshcd_clock_scaling_unprepare(hba, is_writelock);

drivers/ufs/host/ufs-qcom.c

···
 	struct ufs_qcom_host *host = ufshcd_get_variant(hba);
 
 	hba->caps |= UFSHCD_CAP_CLK_GATING | UFSHCD_CAP_HIBERN8_WITH_CLK_GATING;
-	hba->caps |= UFSHCD_CAP_CLK_SCALING;
+	hba->caps |= UFSHCD_CAP_CLK_SCALING | UFSHCD_CAP_WB_WITH_CLK_SCALING;
 	hba->caps |= UFSHCD_CAP_AUTO_BKOPS_SUSPEND;
 	hba->caps |= UFSHCD_CAP_WB_EN;
 	hba->caps |= UFSHCD_CAP_CRYPTO;

include/ufs/ufshcd.h

···
 	 * notification if it is supported by the UFS device.
 	 */
 	UFSHCD_CAP_TEMP_NOTIF				= 1 << 11,
+
+	/*
+	 * Enable WriteBooster when scaling up the clock and disable
+	 * WriteBooster when scaling the clock down.
+	 */
+	UFSHCD_CAP_WB_WITH_CLK_SCALING			= 1 << 12,
 };
 
 struct ufs_hba_variant_params {
···
 static inline bool ufshcd_is_wb_allowed(struct ufs_hba *hba)
 {
 	return hba->caps & UFSHCD_CAP_WB_EN;
+}
+
+static inline bool ufshcd_enable_wb_if_scaling_up(struct ufs_hba *hba)
+{
+	return hba->caps & UFSHCD_CAP_WB_WITH_CLK_SCALING;
 }
 
 #define ufshcd_writel(hba, val, reg)	\