linux-kernel - Re: [PATCH v6 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

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Date:   Tue, 4 Jun 2019 13:54:39 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Pawel Laszczak <pawell@...ence.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "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>,
        "andy.shevchenko@...il.com" <andy.shevchenko@...il.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>, "nm@...com" <nm@...com>,
        Suresh Punnoose <sureshp@...ence.com>,
        "peter.chen@....com" <peter.chen@....com>,
        Rahul Kumar <kurahul@...ence.com>
Subject: Re: [PATCH v6 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

On 04/06/19 1:47 PM, Pawel Laszczak wrote:
>>
>> On 10/04/19 1:18 PM, Pawel Laszczak wrote:
>>> +static void cdns3_wa1_tray_restore_cycle_bit(struct cdns3_device *priv_dev,
>>> +					     struct cdns3_endpoint *priv_ep)
>>> +{
>>> +	int dma_index;
>>> +	u32 doorbell;
>>> +
>>> +	doorbell = !!(readl(&priv_dev->regs->ep_cmd) & EP_CMD_DRDY);
>>
>>> +	dma_index = (readl(&priv_dev->regs->ep_traddr) -
>>> +		    priv_ep->trb_pool_dma) / TRB_SIZE;
>>
>> This gets upgraded to 64-bit by 64-bit division whenever dma_addr_t is
>> 64-bit. That should be avoided. Following diff should fix it.
>> But please review the logic itself. You are subtracting a 64 bit entity
>>from a 32-bit entity. What is guaranteeing that priv_ep->trb_pool_dma is
>> 32-bit?
>>
>> There is one more instance of same issue in cdns3_request_handled().
>>
>> Thanks,
>> Sekhar
>>
>> [1]
>> diff --git a/drivers/usb/cdns3/gadget.c b/drivers/usb/cdns3/gadget.c
>> index bfd5dbf40c7e..e73b618501fb 100644
>> --- a/drivers/usb/cdns3/gadget.c
>> +++ b/drivers/usb/cdns3/gadget.c
>> @@ -749,8 +749,8 @@ static void cdns3_wa1_tray_restore_cycle_bit(struct cdns3_device *priv_dev,
>> 	u32 doorbell;
>>
>> 	doorbell = !!(readl(&priv_dev->regs->ep_cmd) & EP_CMD_DRDY);
>> -	dma_index = (readl(&priv_dev->regs->ep_traddr) -
>> -		    priv_ep->trb_pool_dma) / TRB_SIZE;
>> +	dma_index = readl(&priv_dev->regs->ep_traddr) - priv_ep->trb_pool_dma;
>> +	dma_index /= TRB_SIZE;
> 
> Hi Sekhar,
> 
> In the next latest version I added setting dma and coherent mask to 32-bits as suggested by Roger. 
> Controller can do only 32-bit access.

I think this should work for now except if in some future version of
controller the limitation of 32-bit access is fixed. I guess that might
mean different logic for DMA handling anyway.

> DMA address space should be allocated from first 32 bits of address space. Most significant 32-bit 
> of priv_ep->trb_pool_dma should be zeroed, so I do not assume any issue in this place.
> 
> Have you seen any issue with this on your platform ?

build fails with

ERROR: "__aeabi_uldivmod" [drivers/usb/cdns3/cdns3.ko] undefined!

on 32-bit platforms with ARM LPAE enabled. So please roll in the fix I
suggested.

Thanks,
Sekhar