Fix docs for multiple accelerators (#2804)

Signed-off-by: Andrea Somaini <andrea@somaini.dev>

docs/AddCustomAccelerators.md

@@ -5,6 +5,7 @@ In general, onnx-mlir handles custom accelerators as pluggins which can be turne
 Besides this document, [NNPA accelerator](../src/Accelerators/NNPA) can be used as an example that has been deployed in onnx-mlir.
 
 ## 1. Code folder
+
 In onnx-mlir, all code for an accelerator should be put inside a separate folder under `src/Accelerators`. Thus, the first step to support an accelerator is to create a folder for it inside `src/Accelerators`.
 
 The folder name will be used as the accelerator name in onnx-mlir. In particular, it is used to
@@ -15,22 +16,25 @@ The folder name will be used as the accelerator name in onnx-mlir. In particular
 The folder content is flexible depending on each accelerator. However, we recomment to follow the same structure as the root folder of `onnx-mlir` as much as possbile. This helps maintain the consitency across the whole project.
 
 ### 1.1 Build accelerators in onnx-mlir
-To build accelerators in onnx-mlir, use the cmake variable `ONNX_MLIR_ACCELERATORS` when building onnx-mlir. `ONNX_MLIR_ACCELERATORS` accepts a comma-separated list of accelerator names. For example,
+
+To build accelerators in onnx-mlir, use the cmake variable `ONNX_MLIR_ACCELERATORS` when building onnx-mlir. `ONNX_MLIR_ACCELERATORS` accepts a semicolon-separated list of accelerator names. For example,
 ```bash
 $ cd build
-$ cmake .. -DONNX_MLIR_ACCELERATORS=accel1,accel2
+$ cmake .. -DONNX_MLIR_ACCELERATORS=accel1;accel2
 ```
 
 ### 1.2 Compile a model to run with selected accelerators.
-The compiler command `onnx-mlir` has an option, i.e. `--maccel`, to compile a model for selected accelerators. `--maccel` accepts a comma-separated list of accelerator names. For example,
+
+The compiler command `onnx-mlir` has an option, i.e. `--maccel`, to compile a model for selected accelerators. For each accelerator add a `--maccel=accel_name` entry. For example,
 
 ```bash
-$ onnx-mlir --maccel=accel1,accel2 model.onnx
+$ onnx-mlir --maccel=accel1 --maccel=accel2 model.onnx
 ```
 
 Only built accelerators can be used with `--maccel`.
 
 ### 1.3 Run passes related to selected accelerators.
+
 Passes defined by an accelerator can be run or tested via `onnx-mlir-opt` command by using option `--maccel` which is similar to `--maccel` in `onnx-mlir` (See Sec. [1.2](#1.2-compile-a-model-to-run-with-selected-accelerators)). For example, to call a pass `--optimize-data-layout` defined by accelerator `accel1`:
 
 ```bash
@@ -41,6 +45,24 @@ Only built accelerators can be used with `--maccel`.
 
 ## 2. Code integration
 
+### 2.1 Macro
+
+Each accelerator is required to define a few macros. These needs to be included in [onnx_mlir::accel::Accelerator](../src/Accelerators/Accelerator.hpp). These macros are:
+
+1. `INSTRUMENTSTAGE_ENUM_<accel_name>`
+2. `INSTRUMENTSTAGE_CL_ENUM_<accel_name>`
+3. `PROFILEIR_CL_ENUM_<accel_name>`
+
+Replace `<accel_name>` with the name of the accelerator, for example if your accelerator is named `ACCEL1` use:
+
+```C
+#define INSTRUMENTSTAGE_ENUM_ACCEL1
+#define INSTRUMENTSTAGE_CL_ENUM_ACCEL1
+#define PROFILEIR_CL_ENUM_ACCEL1
+```
+
+### 2.2 Dialects and passes
+
 Writing code in MLIR typically involves desiging dialects and passes. So does supporting an accelerator. Thus, to integrate accelerator code into onnx-mlir is to register dialects and passes in onnx-mlir.
 
 We provide a base class [onnx_mlir::accel::Accelerator](../src/Accelerators/Accelerator.hpp) from which users can define an inherited class and write hooks to register dialects and passes.