Qualcomm AI Engine Direct - fix LPBQ implementation (pytorch#12663)

### Summary
- fix LPBQ and make test case more general

### Test plan
```python
python backends/qualcomm/tests/test_qnn_delegate.py TestQNNQuantizedOperator.test_qnn_backend_conv2d_block -b build-android -s $DEVICE -m SM8750
```

Author: haowhsu-quic

backends/qualcomm/builders/node_visitor.py

@@ -163,10 +163,10 @@ def make_qnn_per_block_config(self, node: torch.fx.Node, quant_attrs: Dict):
             max_scale = scales[ch].reshape(1, -1).amax(dim=-1) / num_steps
             q_scales = torch.clamp(
                 input=scales[ch] / max_scale,
-                min=torch.iinfo(quant_scales_dtype).min,
-                max=torch.iinfo(quant_scales_dtype).max,
+                min=1,
+                max=2**bitwidth_of_scale,
             ).to(quant_scales_dtype)
-            quantized_scales.append(torch.where(q_scales == 0, 1, q_scales))
+            quantized_scales.append(q_scales)
             # symmetric quantization is required
             scale_offset.append(PyQnnWrapper.Qnn_ScaleOffset_t(max_scale, 0))
 

backends/qualcomm/quantizer/observers/per_block_param_observer.py

@@ -35,12 +35,10 @@ def __init__(
             **kwargs,
         )
         self.block_size = block_size
-        # TODO: expand this when QNN starts to support more configurations
-        self.bitwidth_of_scale = 4
-        self.quant_scales_dtype = torch.uint8
+        self.calibrated = False
 
     def forward(self, input: torch.Tensor):
-        if input.numel() == 0:
+        if input.numel() == 0 or self.calibrated:
             return input
 
         input_detached = input.detach()
@@ -66,13 +64,14 @@ def forward(self, input: torch.Tensor):
             self.min_val.copy_(min_val)
             self.max_val.copy_(max_val)
 
+        self.calibrated = True
         return input
 
     def calculate_qparams(self) -> Tuple[torch.Tensor, torch.Tensor]:
         assert hasattr(self, "min_val") and hasattr(
             self, "max_val"
         ), "Expecting the observer has min_val and max_val, please run the observer before calling calculate_qparams"
-        scales, offsets = choose_qparams_affine_with_min_max(
+        return choose_qparams_affine_with_min_max(
             self.min_val,
             self.max_val,
             self.mapping_type,
@@ -86,16 +85,3 @@ def calculate_qparams(self) -> Tuple[torch.Tensor, torch.Tensor]:
             self.preserve_zero,
             self.zero_point_domain,
         )
-        num_channels = scales.shape[0]
-        num_steps = 2**self.bitwidth_of_scale
-        for ch in range(num_channels):
-            max_scale = scales[ch].reshape(1, -1).amax(dim=-1) / num_steps
-            q_scales = torch.clamp(
-                input=scales[ch] / max_scale,
-                min=torch.iinfo(self.quant_scales_dtype).min,
-                max=torch.iinfo(self.quant_scales_dtype).max,
-            ).to(self.quant_scales_dtype)
-            # compensate the error from double quantization
-            scales[ch] = q_scales * max_scale
-
-        return scales, offsets

backends/qualcomm/tests/test_qnn_delegate.py

@@ -1521,20 +1521,7 @@ def test_qnn_backend_conv2d(self):
                 self.lower_module_and_test_output(module, sample_input)
 
     def test_qnn_backend_conv2d_block(self):
-        import numpy as np
-
-        np.random.seed(1)
         o_ch, i_ch, kernel, padding = 32, 512, (1, 1), 0
-        input = (
-            torch.from_numpy(np.random.uniform(-3, 3, size=(1, 1, 32, i_ch)))
-            .to(torch.float)
-            .permute(0, 3, 1, 2)
-        )
-        weight = (
-            torch.from_numpy(np.random.uniform(-3, 3, size=(1, 1, i_ch, o_ch)))
-            .to(torch.float)
-            .permute(3, 2, 0, 1)
-        )
 
         modules = [
             Conv2dSingle(  # noqa: F405
@@ -1551,20 +1538,18 @@ def test_qnn_backend_conv2d_block(self):
                 padding=padding,
             ),
         ]
-        for module in modules:
-            module.conv.weight = torch.nn.Parameter(weight)
 
-        sample_input = (input,)
+        sample_input = (torch.randn(1, i_ch, 1, o_ch),)
         for i, module in enumerate(modules):
             with self.subTest(i=i):
                 # update block size for convolution weight (OIHW)
                 # channel dimension(O) is defaultly sliced in QNN
-                # divide dimension(I) into 4 groups
+                # divide dimension(I) into 16 groups
                 module = self.get_qdq_module(
                     module,
                     sample_input,
                     quant_dtype=QuantDtype.use_16a4w_block,
-                    block_size_map={"conv2d": (1, 128, 1, 1)},
+                    block_size_map={"conv2d": (1, 32, 1, 1)},
                 )
                 self.lower_module_and_test_output(module, sample_input)