ui/pin: check maxlength

src/apps/common/request_pin.py

@@ -16,8 +16,10 @@ async def request_pin(code: int = None) -> str:
     def onchange():
         c = dialog.cancel
         if matrix.pin:
-            c.content = res.load(ui.ICON_CLEAR)
+            c.normal_style = ui.BTN_CLEAR['normal']
+            c.content = res.load(ui.ICON_BACK)
         else:
+            c.normal_style = ui.BTN_CANCEL['normal']
             c.content = res.load(ui.ICON_LOCK)
         c.taint()
         c.render()

src/trezor/ui/pin.py

@@ -67,5 +67,10 @@ class PinMatrix(ui.Widget):
 
     def change(self, pin):
         self.pin = pin
+        for btn in self.pin_buttons:
+            if len(self.pin) == self.maxlength:
+                btn.disable()
+            else:
+                btn.enable()
         if self.onchange:
             self.onchange()