spi: Refactor Conn and ConnCloser into Conn, Port and PortCloser (#131)

This clarifies the difference on ownership and makes it clear that DevParams()
is essentially a 'connection factory'.

The flow is:
  Bus -> Port -> Conn

Doing this caught inconsistencies in the unit tests. Made the structs in spitest
enforce the fact that DevParams() can only be called once.

In a follow up, I'll rename a lot of 'bus' to 'port' to be more consistent but
punting to not make this change unreviewable.

devices/apa102/apa102.go

@@ -293,8 +293,9 @@ func (d *Dev) Halt() error {
 // As per APA102-C spec, the chip's max refresh rate is 400hz.
 // https://en.wikipedia.org/wiki/Flicker_fusion_threshold is a recommended
 // reading.
-func New(s spi.Conn, numLights int, intensity uint8, temperature uint16) (*Dev, error) {
+func New(p spi.Port, numLights int, intensity uint8, temperature uint16) (*Dev, error) {
-	if err := s.DevParams(20000000, spi.Mode3, 8); err != nil {
+	c, err := p.DevParams(20000000, spi.Mode3, 8)
+	if err != nil {
 		return nil, err
 	}
 	// End frames are needed to be able to push enough SPI clock signals due to
@@ -308,7 +309,7 @@ func New(s spi.Conn, numLights int, intensity uint8, temperature uint16) (*Dev,
 	return &Dev{
 		Intensity:   intensity,
 		Temperature: temperature,
-		s:           s,
+		s:           c,
 		numLights:   numLights,
 		rawBuf:      buf,
 		pixels:      buf[4 : 4+4*numLights],

devices/apa102/apa102_test.go

@@ -703,8 +703,8 @@ type configFail struct {
 	spitest.Record
 }
 
-func (c *configFail) DevParams(maxHz int64, mode spi.Mode, bits int) error {
+func (c *configFail) DevParams(maxHz int64, mode spi.Mode, bits int) (spi.Conn, error) {
-	return errors.New("injected error")
+	return nil, errors.New("injected error")
 }
 
 func equalUint16(a, b []uint16) bool {

devices/bme280/bme280.go

@@ -176,12 +176,13 @@ func NewI2C(b i2c.Bus, opts *Opts) (*Dev, error) {
 //
 // BUG(maruel): This code was not tested yet, still waiting for a SPI enabled
 // device in the mail.
-func NewSPI(s spi.Conn, opts *Opts) (*Dev, error) {
+func NewSPI(p spi.Port, opts *Opts) (*Dev, error) {
 	// It works both in Mode0 and Mode3.
-	if err := s.DevParams(10000000, spi.Mode3, 8); err != nil {
+	c, err := p.DevParams(10000000, spi.Mode3, 8)
+	if err != nil {
 		return nil, err
 	}
-	d := &Dev{d: s, isSPI: true}
+	d := &Dev{d: c, isSPI: true}
 	if err := d.makeDev(opts); err != nil {
 		return nil, err
 	}

devices/bme280/bme280_test.go

@@ -545,6 +545,6 @@ type spiFail struct {
 	spitest.Playback
 }
 
-func (s *spiFail) DevParams(maxHz int64, mode spi.Mode, bits int) error {
+func (s *spiFail) DevParams(maxHz int64, mode spi.Mode, bits int) (spi.Conn, error) {
-	return errors.New("failing")
+	return nil, errors.New("failing")
 }

devices/bme280/bme280smoketest/bme280smoketest.go

@@ -67,7 +67,7 @@ func (s *SmokeTest) Run(args []string) (err error) {
 	}
 
 	i2cRecorder := i2ctest.Record{Bus: i2cBus}
-	spiRecorder := spitest.Record{Conn: spiBus}
+	spiRecorder := spitest.Record{Port: spiBus}
 	err = run(&i2cRecorder, &spiRecorder)
 	if len(i2cRecorder.Ops) != 0 {
 		fmt.Printf("I²C recorder Addr: 0x%02X\n", i2cRecorder.Ops[0].Addr)
@@ -119,7 +119,7 @@ func (s *SmokeTest) Run(args []string) (err error) {
 	return err
 }
 
-func run(i2cBus i2c.Bus, spiBus spi.ConnCloser) (err error) {
+func run(i2cBus i2c.Bus, spiBus spi.PortCloser) (err error) {
 	opts := &bme280.Opts{
 		Temperature: bme280.O16x,
 		Pressure:    bme280.O16x,

devices/lepton/lepton.go

@@ -94,17 +94,17 @@ type Dev struct {
 // Maximum I²C speed is 1Mhz.
 //
 // MOSI is not used and should be grounded.
-func New(s spi.Conn, i i2c.Bus, cs gpio.PinOut) (*Dev, error) {
+func New(p spi.Port, i i2c.Bus, cs gpio.PinOut) (*Dev, error) {
 	// Sadly the Lepton will unconditionally send 27fps, even if the effective
 	// rate is 9fps.
 	mode := spi.Mode3
 	if cs == nil {
 		// Query the CS pin before disabling it.
-		p, ok := s.(spi.Pins)
+		pins, ok := p.(spi.Pins)
 		if !ok {
 			return nil, errors.New("lepton: require manual access to the CS pin")
 		}
-		cs = p.CS()
+		cs = pins.CS()
 		if cs == gpio.INVALID {
 			return nil, errors.New("lepton: require manual access to a valid CS pin")
 		}
@@ -112,7 +112,8 @@ func New(s spi.Conn, i i2c.Bus, cs gpio.PinOut) (*Dev, error) {
 	}
 	// TODO(maruel): Switch to 16 bits per word, so that big endian 16 bits word
 	// decoding is done by the SPI driver.
-	if err := s.DevParams(20000000, mode, 8); err != nil {
+	s, err := p.DevParams(20000000, mode, 8)
+	if err != nil {
 		return nil, err
 	}
 	c, err := cci.New(i)

devices/lepton/lepton_test.go

@@ -370,7 +370,7 @@ type spiStream struct {
 	err    error
 }
 
-func (s *spiStream) DevParams(maxHz int64, mode spi.Mode, bits int) error {
+func (s *spiStream) DevParams(maxHz int64, mode spi.Mode, bits int) (spi.Conn, error) {
 	if maxHz != 20000000 {
 		s.t.Fatal(maxHz)
 	}
@@ -380,7 +380,7 @@ func (s *spiStream) DevParams(maxHz int64, mode spi.Mode, bits int) error {
 	if bits != 8 {
 		s.t.Fatal(bits)
 	}
-	return s.err
+	return s, s.err
 }
 
 func (s *spiStream) Tx(w, r []byte) error {

devices/ssd1306/ssd1306.go

@@ -122,7 +122,7 @@ type Dev struct {
 // The RES (reset) pin can be used outside of this driver but is not supported
 // natively. In case of external reset via the RES pin, this device drive must
 // be reinstantiated.
-func NewSPI(s spi.Conn, dc gpio.PinOut, w, h int, rotated bool) (*Dev, error) {
+func NewSPI(p spi.Port, dc gpio.PinOut, w, h int, rotated bool) (*Dev, error) {
 	if dc == gpio.INVALID {
 		return nil, errors.New("ssd1306: use nil for dc to use 3-wire mode, do not use gpio.INVALID")
 	}
@@ -133,10 +133,11 @@ func NewSPI(s spi.Conn, dc gpio.PinOut, w, h int, rotated bool) (*Dev, error) {
 	} else if err := dc.Out(gpio.Low); err != nil {
 		return nil, err
 	}
-	if err := s.DevParams(3300000, spi.Mode0, bits); err != nil {
+	c, err := p.DevParams(3300000, spi.Mode0, bits)
+	if err != nil {
 		return nil, err
 	}
-	return newDev(s, w, h, rotated, true, dc)
+	return newDev(c, w, h, rotated, true, dc)
 }
 
 // NewI2C returns a Dev object that communicates over I²C to a SSD1306 display

devices/ssd1306/ssd1306_test.go

@@ -575,8 +575,8 @@ type configFail struct {
 	spitest.Record
 }
 
-func (c *configFail) DevParams(maxHz int64, mode spi.Mode, bits int) error {
+func (c *configFail) DevParams(maxHz int64, mode spi.Mode, bits int) (spi.Conn, error) {
-	return errors.New("injected error")
+	return nil, errors.New("injected error")
 }
 
 type failPin struct {

devices/ssd1306/ssd1306smoketest/ssd1306smoketest.go

@@ -97,7 +97,7 @@ func (s *SmokeTest) Run(args []string) (err error) {
 	}
 
 	i2cRecorder := i2ctest.Record{Bus: i2cBus}
-	spiRecorder := spitest.Record{Conn: spiBus}
+	spiRecorder := spitest.Record{Port: spiBus}
 	err = s.run(&i2cRecorder, &spiRecorder, dc, *w, *h, *rotated)
 	if len(i2cRecorder.Ops) != 0 {
 		fmt.Printf("I²C recorder Addr: 0x%02X\n", i2cRecorder.Ops[0].Addr)
@@ -149,7 +149,7 @@ func (s *SmokeTest) Run(args []string) (err error) {
 	return err
 }
 
-func (s *SmokeTest) run(i2cBus i2c.Bus, spiBus spi.ConnCloser, dc gpio.PinOut, w, h int, rotated bool) (err error) {
+func (s *SmokeTest) run(i2cBus i2c.Bus, spiBus spi.PortCloser, dc gpio.PinOut, w, h int, rotated bool) (err error) {
 	s.timings = make([]time.Duration, 2)
 	start := time.Now()
 	i2cDev, err2 := ssd1306.NewI2C(i2cBus, w, h, rotated)