media: atomisp: Remove non working doorbell check from punit_ddr_dvfs_enable()

punit_ddr_dvfs_enable() is only used on CHT devices and there dmesg
gets filled with: "DDR DVFS, door bell is not cleared within 3ms"
messages, so clearly the doorbell checking is not working.

This check was added by:
https://github.com/intel/ProductionKernelQuilts/blob/master/uefi/cht-m1stable/patches/cam-0340-atomisp-add-door-bell-for-ddr-dvfs-on-cht.patch

Which commit message says: "PUNIT interface added to check Req_ACK
of freq status". This suggests that the doorbell mechanism may only
be available with certain PUNIT fw versions and it seems that
many CHT devices do not have this fw version; that or the doorbell
mechanism is not working for other reasons.

Revert cam-0340-atomisp-add-door-bell-for-ddr-dvfs-on-cht.patch,
replacing the doorbell check with a msleep(20) this fixes dmesg
getting filled with error messages.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/staging/media/atomisp/pci/atomisp_v4l2.c

@@ -638,27 +638,16 @@ static int atomisp_mrfld_pre_power_down(struct atomisp_device *isp)
 */
 static void punit_ddr_dvfs_enable(bool enable)
 {
-	int door_bell = 1 << 8;
-	int max_wait = 30;
 	int reg;
 
 	iosf_mbi_read(BT_MBI_UNIT_PMC, MBI_REG_READ, MRFLD_ISPSSDVFS, &reg);
 	if (enable) {
 		reg &= ~(MRFLD_BIT0 | MRFLD_BIT1);
 	} else {
-		reg |= (MRFLD_BIT1 | door_bell);
+		reg |= MRFLD_BIT1;
 		reg &= ~(MRFLD_BIT0);
 	}
 	iosf_mbi_write(BT_MBI_UNIT_PMC, MBI_REG_WRITE, MRFLD_ISPSSDVFS, reg);
-
-	/* Check Req_ACK to see freq status, wait until door_bell is cleared */
-	while ((reg & door_bell) && max_wait--) {
-		iosf_mbi_read(BT_MBI_UNIT_PMC, MBI_REG_READ, MRFLD_ISPSSDVFS, &reg);
-		usleep_range(100, 500);
-	}
-
-	if (max_wait == -1)
-		pr_info("DDR DVFS, door bell is not cleared within 3ms\n");
 }
 
 static int atomisp_mrfld_power(struct atomisp_device *isp, bool enable)
@@ -671,8 +660,10 @@ static int atomisp_mrfld_power(struct atomisp_device *isp, bool enable)
 	dev_dbg(isp->dev, "IUNIT power-%s.\n", enable ? "on" : "off");
 
 	/* WA for P-Unit, if DVFS enabled, ISP timeout observed */
-	if (IS_CHT && enable)
+	if (IS_CHT && enable) {
 		punit_ddr_dvfs_enable(false);
+		msleep(20);
+	}
 
 	/*
 	 * FIXME:WA for ECS28A, with this sleep, CTS