On 21-01-14 06:16:18, Thinh Nguyen wrote: > Hi Peter, > > Peter Chen wrote: > > On 21-01-13 18:53:14, Thinh Nguyen wrote: > >> If a gadget supports SuperSpeed Plus, then it may operate in different > >> sublink speeds. For example, if the gadget supports SuperSpeed Plus > >> gen2x2, then it can support 2 sublink speeds gen1 and gen2. Inform the > >> host of these speeds in the BOS descriptor. > >> > > Hi Thinh, > > > > I read USB 3.2 spec: ch9.6.2.5 SuperSpeedPlus USB Device Capability > > > > Symmetric. Rx and Tx Sublinks have the same number of lanes and operate > > at the same speed. > > Asymmetric. Rx and Tx Sublink have different number of lanes and/or > > operate at different speeds. > > > > Why your below cases are all for symmetric, at least, the example 3 > > is asymmetric, it has different speed for sublink pairs? > > Does your below cases are specification defined or user defined? > > USB 3.2 spec section 8.5.6.7: > Asymmetric lane types are only for SuperSpeed Interchip (SSIC). IMO, > It's unlikely that SSIC user will use Linux kernel. We can extend and > update the gadget framework if there's any use case for that. > > > > > >> Use 1 SSID if the gadget supports up to gen2x1, or not specified: > >> - SSID 0 for symmetric RX/TX sublink speed of 10 Gbps. > >> > >> Use 1 SSID if the gadget supports up to gen1x2: > >> - SSID 0 for symmetric RX/TX sublink speed of 5 Gbps. > >> > >> Use 2 SSIDs if the gadget supports up to gen2x2: > >> - SSID 0 for symmetric RX/TX sublink speed of 5 Gbps. > > Why SSID 0 is not 10Gbps? > > SSID 0 and 1 are arbitrary, we can do 0 for 10Gbps. There's no > constraint or standard from the USB 3.2 spec. However, you need to set > the descriptor wFunctionalitySupport.SSID to be the minimum lane speed > SSID it supports. Using SSID 0 makes it easier since we don't have to > condition it for multiple SSIDs. > > >> - SSID 1 for symmetric RX/TX sublink speed of 10 Gbps. > > Besides, would you give me an example what kinds of system design > > will use below sublink speed? > > - SSID 0 for symmetric RX/TX sublink speed of 5 Gbps. > > - SSID 1 for symmetric RX/TX sublink speed of 10 Gbps. > > > > Peter > > These 2 SSIDs indicate that the device is capable of running in gen1 and > gen2 in SSP. > Hi Thinh, I am puzzled, GEN2 is back compatible for GEN1. Then, what's the usage of this descriptor, what kinds of specific information the host wants to get? I think the host wants to get if two pairs of tx/rx are supported, that is what USB 3.2 adds. -- Thanks, Peter Chen
