Add two space saving knobs

* Reduce the number of supported HID reports of IDs per descriptor.
  This saves ~200 bytes in the default HID objects.
* (Not enabled) Compute QSTR attrs on init. This trades 1k RAM for
  flash. Flash is the default (1).

Author: tannewt

ports/atmel-samd/mpconfigport.h

@@ -61,6 +61,9 @@
 
 #define MICROPY_FATFS_EXFAT 0
 
+// Only support simpler HID descriptors on SAMD21.
+#define CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR (1)
+
 #endif // SAMD21
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////

py/circuitpy_mpconfig.h

@@ -717,6 +717,13 @@ void supervisor_run_background_tasks_if_tick(void);
 
 #define CIRCUITPY_VERBOSE_BLE 0
 
+// This trades ~1k flash space (1) for that much in RAM plus the cost to compute
+// the values once on init (0). Only turn it off, when you really need the flash
+// space and are willing to trade the RAM.
+#ifndef CIRCUITPY_PRECOMPUTE_QSTR_ATTR
+#define CIRCUITPY_PRECOMPUTE_QSTR_ATTR (1)
+#endif
+
 // USB settings
 
 // If the port requires certain USB endpoint numbers, define these in mpconfigport.h.
@@ -761,6 +768,16 @@ void supervisor_run_background_tasks_if_tick(void);
 #define USB_HID_EP_NUM_IN (0)
 #endif
 
+// The most complicated device currently known of is the head and eye tracker, which requires 5
+// report ids.
+// https://usb.org/sites/default/files/hutrr74_-_usage_page_for_head_and_eye_trackers_0.pdf
+// The default descriptors only use 1, so that is the minimum.
+#ifndef CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR
+#define CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR (6)
+#elif CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR < 1
+#error "CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR must be at least 1"
+#endif
+
 #ifndef USB_MIDI_EP_NUM_OUT
 #define USB_MIDI_EP_NUM_OUT (0)
 #endif

py/qstr.c

@@ -77,7 +77,8 @@ mp_uint_t qstr_compute_hash(const byte *data, size_t len) {
     return hash;
 }
 
-const qstr_attr_t mp_qstr_const_attr[] = {
+#if CIRCUITPY_PRECOMPUTE_QSTR_ATTR
+const qstr_attr_t mp_qstr_const_attr[MP_QSTRnumber_of] = {
     #ifndef NO_QSTR
 #define QDEF(id, hash, len, str) { hash, len },
 #define TRANSLATION(id, length, compressed ...)
@@ -86,6 +87,9 @@ const qstr_attr_t mp_qstr_const_attr[] = {
 #undef QDEF
     #endif
 };
+#else
+qstr_attr_t mp_qstr_const_attr[MP_QSTRnumber_of];
+#endif
 
 const qstr_pool_t mp_qstr_const_pool = {
     NULL,               // no previous pool
@@ -115,6 +119,16 @@ void qstr_init(void) {
     MP_STATE_VM(last_pool) = (qstr_pool_t *)&CONST_POOL; // we won't modify the const_pool since it has no allocated room left
     MP_STATE_VM(qstr_last_chunk) = NULL;
 
+    #if CIRCUITPY_PRECOMPUTE_QSTR_ATTR == 0
+    if (mp_qstr_const_attr[MP_QSTR_circuitpython].len == 0) {
+        for (size_t i = 0; i < mp_qstr_const_pool.len; i++) {
+            size_t len = strlen(mp_qstr_const_pool.qstrs[i]);
+            mp_qstr_const_attr[i].hash = qstr_compute_hash((const byte *)mp_qstr_const_pool.qstrs[i], len);
+            mp_qstr_const_attr[i].len = len;
+        }
+    }
+    #endif
+
     #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
     mp_thread_mutex_init(&MP_STATE_VM(qstr_mutex));
     #endif

shared-module/usb_hid/Device.c

@@ -81,7 +81,7 @@ const usb_hid_device_obj_t usb_hid_device_keyboard_obj = {
     .usage = 0x06,
     .num_report_ids = 1,
     .report_ids = { 0x01, },
-    .in_report_lengths = { 8, 0, 0, 0, 0, 0, },
+    .in_report_lengths = { 8, },
     .out_report_lengths = { 1, },
 };
 
@@ -131,7 +131,7 @@ const usb_hid_device_obj_t usb_hid_device_mouse_obj = {
     .usage = 0x02,
     .num_report_ids = 1,
     .report_ids = { 0x02, },
-    .in_report_lengths = { 4, 0, 0, 0, 0, 0, },
+    .in_report_lengths = { 4, },
     .out_report_lengths = { 0, },
 };
 
@@ -160,7 +160,7 @@ const usb_hid_device_obj_t usb_hid_device_consumer_control_obj = {
     .usage = 0x01,
     .num_report_ids = 1,
     .report_ids = { 0x03 },
-    .in_report_lengths = { 2, 0, 0, 0, 0, 0, },
+    .in_report_lengths = { 2, },
     .out_report_lengths = { 0, },
 };
 
@@ -170,7 +170,7 @@ STATIC size_t get_report_id_idx(usb_hid_device_obj_t *self, size_t report_id) {
             return i;
         }
     }
-    return MAX_REPORT_IDS_PER_DESCRIPTOR;
+    return CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR;
 }
 
 // See if report_id is used by this device. If it is -1, then return the sole report id used by this device,
@@ -180,16 +180,16 @@ uint8_t common_hal_usb_hid_device_validate_report_id(usb_hid_device_obj_t *self,
         return self->report_ids[0];
     }
     if (!(report_id_arg >= 0 &&
-          get_report_id_idx(self, (size_t)report_id_arg) < MAX_REPORT_IDS_PER_DESCRIPTOR)) {
+          get_report_id_idx(self, (size_t)report_id_arg) < CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR)) {
         mp_raise_ValueError_varg(translate("Invalid %q"), MP_QSTR_report_id);
     }
     return (uint8_t)report_id_arg;
 }
 
 void common_hal_usb_hid_device_construct(usb_hid_device_obj_t *self, mp_obj_t report_descriptor, uint8_t usage_page, uint8_t usage, size_t num_report_ids, uint8_t *report_ids, uint8_t *in_report_lengths, uint8_t *out_report_lengths) {
-    if (num_report_ids > MAX_REPORT_IDS_PER_DESCRIPTOR) {
+    if (num_report_ids > CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR) {
         mp_raise_ValueError_varg(translate("More than %d report ids not supported"),
-            MAX_REPORT_IDS_PER_DESCRIPTOR);
+            CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR);
     }
 
     // report buffer pointers are NULL at start, and are created when USB is initialized.

shared-module/usb_hid/Device.h

@@ -32,21 +32,16 @@
 
 #include "py/obj.h"
 
-// The most complicated device currently known of is the head and eye tracker, which requires 5
-// report ids.
-// https://usb.org/sites/default/files/hutrr74_-_usage_page_for_head_and_eye_trackers_0.pdf
-#define MAX_REPORT_IDS_PER_DESCRIPTOR (6)
-
 typedef struct  {
     mp_obj_base_t base;
     // Python buffer object whose contents are the descriptor.
     const uint8_t *report_descriptor;
-    uint8_t *in_report_buffers[MAX_REPORT_IDS_PER_DESCRIPTOR];
-    uint8_t *out_report_buffers[MAX_REPORT_IDS_PER_DESCRIPTOR];
+    uint8_t *in_report_buffers[CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR];
+    uint8_t *out_report_buffers[CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR];
     uint16_t report_descriptor_length;
-    uint8_t report_ids[MAX_REPORT_IDS_PER_DESCRIPTOR];
-    uint8_t in_report_lengths[MAX_REPORT_IDS_PER_DESCRIPTOR];
-    uint8_t out_report_lengths[MAX_REPORT_IDS_PER_DESCRIPTOR];
+    uint8_t report_ids[CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR];
+    uint8_t in_report_lengths[CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR];
+    uint8_t out_report_lengths[CIRCUITPY_USB_HID_MAX_REPORT_IDS_PER_DESCRIPTOR];
     uint8_t usage_page;
     uint8_t usage;
     uint8_t num_report_ids;