linux-kernel - RE: [PATCH v9 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

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Message-ID: <VI1PR04MB53279117788B7D7CC3080B398BD30@VI1PR04MB5327.eurprd04.prod.outlook.com>
Date:   Mon, 12 Aug 2019 01:55:35 +0000
From:   Peter Chen <peter.chen@....com>
To:     Pawel Laszczak <pawell@...ence.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "rogerq@...com" <rogerq@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jbergsagel@...com" <jbergsagel@...com>,
        "nsekhar@...com" <nsekhar@...com>, "nm@...com" <nm@...com>,
        Suresh Punnoose <sureshp@...ence.com>,
        Jayshri Dajiram Pawar <jpawar@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>
Subject: RE: [PATCH v9 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

  
> 
> Yes, driver frees not used buffers here.
> I think that it's the safest place for this purpose.
> 
> >
> >>>> +				dma_free_coherent(priv_dev->sysdev, buf-
> >size,
> >>>> +						  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.
> >> 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