Yes, driver frees not used buffers here.
I think that it's the safest place for this purpose.

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+				dma_free_coherent(priv_dev->sysdev, buf-

size,

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+						  buf->buf,
+						  buf->dma);
+				spin_lock_irqsave(&priv_dev->lock, flags);
+
+				kfree(buf);

why do you even need this "garbage collector"?

I need to free not used memory. The once allocated buffer will be
associated with request, but if request.length will be increased in
usb_request then driver will must allocate the  bigger buffer. As I
remember I couldn't call dma_free_coherent in interrupt context so I
had to move it to thread handled. This flag was used to avoid going through

whole  aligned_buf_list  every time.

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In most cases this part will never called int this place

Did you try, btw, setting the quirk flag which tells gadget drivers to
always allocate buffers aligned to MaxPacketSize? Wouldn't that be enough?

If found only  quirk_ep_out_aligned_size flag, but it align only buffer size.

DMA used by this controller must have buffer address aligned to 8.
I think that on most architecture kmalloc should guarantee such aligned.
The problem was detected on NXP testing board.
On my board all buffer address are alignment at least to 8.

 
This un-aligned request buffer address for 8 occurs for Ethernet Gadget (eg, NCM),
it allocates socket buffer with NET_IP_ALIGN, so the last byte of buffer address
is always 2. Although this can be workaround by setting quirk_avoids_skb_reserve,
but we are not sure if all gadget request buffers can be 8 or Max Packet Size aligned.

Peter