Understanding UFS Descriptors

Understanding UFS Descriptors

Structured data entities known as UFS (Universal Flash Storage) descriptors offer vital device information in an easily comprehensible format. These descriptors, which are accessed via QUERY REQUEST UPIU (UFS Protocol Information Unit) packets, are essential for UFS communication and device configuration.

What is a Descriptor?

In essence, a descriptor is a data structure with a preset layout. Since these structures can be accessed separately without the need for additional descriptors, they are independently addressable. However, descriptors can also be linked hierarchically, with top-level descriptors using parameters defined within them to link to other descriptors.

Key Features of Descriptors

• Addressable and Independent: Each descriptor can be uniquely accessed.
• Variable Sizes: Descriptors can range from 2 bytes to 255 bytes.
  • A 2-byte descriptor is considered empty.
• Format: Every descriptor begins with two critical elements:
  1. Length Byte (1st byte): Indicates the total size of the descriptor, including the length byte itself.
  2. Type Identification (2nd byte): Specifies the type or classification of the descriptor.
• Read Access: Descriptors can be partially read, but reading always starts at an offset of 00h.

Types of Descriptors

Descriptors serve as blocks or pages of parameters that describe specific aspects of a UFS device. Common types of descriptors include:

1. Device Descriptor: Provides general details about the UFS device.
2. Configuration Descriptor: Describes and allows modification of device configurations.
3. Unit Descriptor: Contains information specific to storage units within the device.

Modifying Descriptors

While all descriptors are readable, their write permissions can vary:

• Some descriptors are write-once, meaning they cannot be modified after their initial write.
• Others may have written protection mechanisms to prevent unauthorized changes.

The Configuration Descriptor is particularly notable because it is writeable. It allows the device’s configuration—initially set by the manufacturer—to be modified as needed. This flexibility enables customization and tuning of the device’s behavior to suit specific requirements.

Summary

UFS descriptors, which offer a structured method of accessing and modifying device parameters, are essential to device communication. Descriptors enable effective management and configuration of UFS devices due to their structured format, independent addressability, and variety of permissions. By describing the device as a whole or concentrating on specific units, descriptors serve as the foundation for UFS data interaction.