Re: simple example of pci driver with dma

[Yan Vugenfirer]

Hi Shaked,

In the prob function, before you are trying to do any DMA operations with your 
device, you should call pci_enable_device and then pci_set_master. Also you 
might need to map the resources of your device.
Check PCI driver documentation: 
https://lxr.missinglinkelectronics.com/linux/Documentation/PCI/pci.rst#L199

Best regards,
Yan.

> On 29 Oct 2020, at 10:32 PM, Shaked Matzner <shaked.m@neuroblade.ai> wrote:
> 
> Hey Peter,
> Currently I have this test in the driver which allocates data, assign it to 
> default value config source as the BASE address of dma, dest as the physical 
> address which I got from dma_alloc_coherent, set the count and assign the 
> command to raise interrupt and read,the piece of code used is something like 
> this(this a test performed from the probe function of the driver)
>                                                 vaddr_to = 
> dma_alloc_coherent(&(dev->dev), 4, &dma_handle_to, GFP_ATOMIC |GFP_KERNEL);
>             *((volatile int*)vaddr_to) = 0xff;
>                                                 test->vaddr_to = vaddr_to;
>                                                 dev_info(&(dev->dev), 
> "vaddr_to = %px\n", vaddr_to);
>                                                 dev_info(&(dev->dev), 
> "dma_handle_to = %llx\n", (unsigned long long)dma_handle_to);
>                                                 iowrite32(DMA_BASE, mmio + 
> IO_DMA_SRC);
>                                                 iowrite32((u32)dma_handle_to, 
> mmio + IO_DMA_DST);
>                                                 iowrite32(SIZE, mmio + 
> IO_DMA_CNT);
>                                                iowrite32(DMA_CMD | 
> DMA_FROM_DEV | DMA_IRQ, mmio + IO_DMA_CMD);
> Where and when should the pci_set_master hould be called?
> Thanks,
>              Shaked Matzner
>  
> From: Peter Maydell <peter.maydell@linaro.org> 
> Sent: Thursday, October 29, 2020 5:46 PM
> To: Shaked Matzner <shaked.m@neuroblade.ai>
> Cc: qemu-devel@nongnu.org
> Subject: Re: simple example of pci driver with dma
>  
> 
> IRONSCALES couldn't recognize this email as this is the first time you 
> received an email from this sender peter.maydell@linaro.org
>  
> [EXTERNAL]
> 
> On Thu, 29 Oct 2020 at 14:59, Shaked Matzner wrote:
> > however the value I get is still 255(0xff) and not 18(0x12) probably I've 
> > missed something but when the interrupt is called the transfer to the RAM 
> > address should be completed, however it seems like the dma_write_buffer 
> > function from the device does not perform any transfer. What Am I missing?
> 
> The usual mistake is forgetting in the guest code to program the
> PCI device to enable bus mastering by setting the Bus Master bit
> in the Command register in the PCI config space registers for
> the device. Unless you do that then all DMA attempts will fail
> (same as on real h/w). In the Linux kernel the function for this
> is pci_set_master(), I think.
> 
> thanks
> -- PMM 
> 
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