Re: [REGRESSION] usb: gadget: f_fs: Allow scatter-gather buffers

[Andrzej Pietrasiewicz]

Hi,

W dniu 20.05.2019 o 23:52, Yang, Fei pisze:

One question that comes to my mind is this: Does the USB

<snip>

One of the problems appears to be that req->num_mapped_sgs was left 
uninitialized. I made the following change and got a lot more requests completed.
However this change is not sufficient to solve the adb issue, the usb requests 
would eventually get stuck without getting a matching 
ffs_epfile_async_io_complete.

@@ -1067,6 +1067,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct 
ffs_io_data *io_data)
                         req->buf = NULL;
                         req->sg = io_data->sgt.sgl;
                         req->num_sgs = io_data->sgt.nents;
+                       req->num_mapped_sgs = req->num_sgs;
                 } else {
                         req->buf = data;
                 }
@@ -1110,6 +1111,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct 
ffs_io_data *io_data)
                         req->buf = NULL;
                         req->sg = io_data->sgt.sgl;
                         req->num_sgs = io_data->sgt.nents;
+                       req->num_mapped_sgs = req->num_sgs;
                 } else {
                         req->buf = data;
                 }

Isn't num_mapped_sgs meant to be set by drivers/usb/gadget/udc/core.c?

And the comment in include/linux/usb/gadget.h says "internal".

One thing that becomes evident now is that adb uses async io.
It seems that interaction of async io and s-g mode should be further
investigated.

Andrzej