Re: [RFC PATCH] usb: gadget: f_tcm: Added DMA32 flag while allocation of command buffer

[Roger Quadros <rogerq@xxxxxx>]

Jayshri,

On 14/11/2019 04:50, Peter Chen wrote:
> On 19-11-13 10:24:32, Jayshri Pawar wrote:
> > There is a problem when function driver allocate memory for buffer
> > used by DMA from outside dma_mask space.
> > It appears during testing f_tcm driver with cdns3 controller.
> > In the result cdns3 driver was not able to map virtual buffer to DMA.
> > This fix should be improved depending on dma_mask associated with device.
> > Adding GFP_DMA32 flag while allocationg command data buffer only for 32
> > bit controllers.
>
> Hi Jayshri,
>
> This issue should be fixed by setting DMA_MASK correctly for controller,
> you can't limit user's memory region. At usb_ep_queue, the UDC driver
> will call DMA MAP API, for Cadence, it is usb_gadget_map_request_by_dev.
> For the system without SMMU (IO-MMU), it will use swiotlb to make sure
> the data buffer used for DMA transfer is within DMA mask for controller,
> There is a reserved low memory region for debounce buffer in swiotlb
> use case.

/**
 * struct usb_request - describes one i/o request
 * @buf: Buffer used for data.  Always provide this; some controllers
 *	only use PIO, or don't use DMA for some endpoints.
 * @dma: DMA address corresponding to 'buf'.  If you don't set this
 *	field, and the usb controller needs one, it is responsible
 *	for mapping and unmapping the buffer.
<snip>
 */

So if dma is not set in the usb_request then controller driver is
responsible to do a dma_map of the buffer pointed by 'buf' before
it attemps to do DMA. This should take care of DMA mask and swiotlb.

This patch is not correct.

cheers,
-roger

> Peter
>
> > Signed-off-by: Pawel Laszczak <pawell@xxxxxxxxxxx>
> > Signed-off-by: Jayshri Pawar <jpawar@xxxxxxxxxxx>
> > ---
> >   drivers/usb/gadget/function/f_tcm.c | 20 ++++++++++++++------
> >   include/linux/usb/gadget.h          |  2 ++
> >   2 files changed, 16 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/function/f_tcm.c b/drivers/usb/gadget/function/f_tcm.c
> > index 36504931b2d1..a78d5fad3d84 100644
> > --- a/drivers/usb/gadget/function/f_tcm.c
> > +++ b/drivers/usb/gadget/function/f_tcm.c
> > @@ -213,7 +213,8 @@ static int bot_send_read_response(struct usbg_cmd *cmd)
> >   	}
> >   
> >   	if (!gadget->sg_supported) {
> > -		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_ATOMIC);
> > +		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_ATOMIC |
> > +					gadget->dma_flag);
> >   		if (!cmd->data_buf)
> >   			return -ENOMEM;
> >   
> > @@ -257,7 +258,8 @@ static int bot_send_write_request(struct usbg_cmd *cmd)
> >   	}
> >   
> >   	if (!gadget->sg_supported) {
> > -		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_KERNEL);
> > +		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_KERNEL |
> > +					gadget->dma_flag);
> >   		if (!cmd->data_buf)
> >   			return -ENOMEM;
> >   
> > @@ -305,6 +307,7 @@ static void bot_cmd_complete(struct usb_ep *ep, struct usb_request *req)
> >   static int bot_prepare_reqs(struct f_uas *fu)
> >   {
> >   	int ret;
> > +	struct usb_gadget *gadget = fuas_to_gadget(fu);
> >   
> >   	fu->bot_req_in = usb_ep_alloc_request(fu->ep_in, GFP_KERNEL);
> >   	if (!fu->bot_req_in)
> > @@ -327,7 +330,8 @@ static int bot_prepare_reqs(struct f_uas *fu)
> >   	fu->bot_status.req->complete = bot_status_complete;
> >   	fu->bot_status.csw.Signature = cpu_to_le32(US_BULK_CS_SIGN);
> >   
> > -	fu->cmd.buf = kmalloc(fu->ep_out->maxpacket, GFP_KERNEL);
> > +	fu->cmd.buf = kmalloc(fu->ep_out->maxpacket, GFP_KERNEL |
> > +				gadget->dma_flag);
> >   	if (!fu->cmd.buf)
> >   		goto err_buf;
> >   
> > @@ -515,7 +519,8 @@ static int uasp_prepare_r_request(struct usbg_cmd *cmd)
> >   	struct uas_stream *stream = cmd->stream;
> >   
> >   	if (!gadget->sg_supported) {
> > -		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_ATOMIC);
> > +		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_ATOMIC |
> > +					gadget->dma_flag);
> >   		if (!cmd->data_buf)
> >   			return -ENOMEM;
> >   
> > @@ -763,11 +768,13 @@ static int uasp_alloc_stream_res(struct f_uas *fu, struct uas_stream *stream)
> >   
> >   static int uasp_alloc_cmd(struct f_uas *fu)
> >   {
> > +	struct usb_gadget *gadget = fuas_to_gadget(fu);
> >   	fu->cmd.req = usb_ep_alloc_request(fu->ep_cmd, GFP_KERNEL);
> >   	if (!fu->cmd.req)
> >   		goto err;
> >   
> > -	fu->cmd.buf = kmalloc(fu->ep_cmd->maxpacket, GFP_KERNEL);
> > +	fu->cmd.buf = kmalloc(fu->ep_cmd->maxpacket, GFP_KERNEL |
> > +				gadget->dma_flag);
> >   	if (!fu->cmd.buf)
> >   		goto err_buf;
> >   
> > @@ -980,7 +987,8 @@ static int usbg_prepare_w_request(struct usbg_cmd *cmd, struct usb_request *req)
> >   	struct usb_gadget *gadget = fuas_to_gadget(fu);
> >   
> >   	if (!gadget->sg_supported) {
> > -		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_ATOMIC);
> > +		cmd->data_buf = kmalloc(se_cmd->data_length, GFP_ATOMIC |
> > +					gadget->dma_flag);
> >   		if (!cmd->data_buf)
> >   			return -ENOMEM;
> >   
> > diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
> > index 124462d65eac..d6c9cd222600 100644
> > --- a/include/linux/usb/gadget.h
> > +++ b/include/linux/usb/gadget.h
> > @@ -373,6 +373,7 @@ struct usb_gadget_ops {
> >    * @connected: True if gadget is connected.
> >    * @lpm_capable: If the gadget max_speed is FULL or HIGH, this flag
> >    *	indicates that it supports LPM as per the LPM ECN & errata.
> > + * @dma_flag: dma zone to be used for buffer allocation.
> >    *
> >    * Gadgets have a mostly-portable "gadget driver" implementing device
> >    * functions, handling all usb configurations and interfaces.  Gadget
> > @@ -427,6 +428,7 @@ struct usb_gadget {
> >   	unsigned			deactivated:1;
> >   	unsigned			connected:1;
> >   	unsigned			lpm_capable:1;
> > +	unsigned int			dma_flag;
> >   };
> >   #define work_to_gadget(w)	(container_of((w), struct usb_gadget, work))
> >   
> > --
> > 2.20.1

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