linux-kernel - Re: [PATCH] PCI: endpoint: pci-epf-test: Move DMA check into read/write/copy functions

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Message-ID: <7a44e4cb-9f91-47e3-badc-8c6d406d1ea0@kernel.org>
Date: Wed, 7 Aug 2024 09:08:29 -0700
From: Damien Le Moal <dlemoal@...nel.org>
To: Rick Wertenbroek <rick.wertenbroek@...il.com>, rick.wertenbroek@...g-vd.ch
Cc: alberto.dassatti@...g-vd.ch,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Niklas Cassel <cassel@...nel.org>,
 Frank Li <Frank.Li@....com>, Lars-Peter Clausen <lars@...afoo.de>,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: endpoint: pci-epf-test: Move DMA check into
 read/write/copy functions

On 2024/08/06 9:27, Rick Wertenbroek wrote:
> The test for a DMA transfer was done in pci_epf_test_cmd_handler, which
> if not supported would lead to the endpoint function just printing an
> error message and waiting for further commands. This would leave the
> host side PCI driver waiting for an interrupt because the call to
> pci_epf_test_raise_irq is skipped. The host side driver
> drivers/misc/pci_endpoint_test.c would hang indefinitely when sending
> a transfer request with DMA if the endpoint does not support it.
> This is because wait_for_completion() is used in the host side driver.
> 
> Move the DMA check into the read/write/copy functions so that they
> report a transfer (IO) error so that pci_epf_test_raise_irq() is
> called when a transfer with DMA is requested, even if unsupported.
> 
> The host side driver will still report an error on transfer thanks
> to the checksum, because no data was moved, but will not hang anymore
> waiting for an interrupt that will never arrive.
> 
> Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>
> ---
>  drivers/pci/endpoint/functions/pci-epf-test.c | 29 +++++++++++++++----
>  1 file changed, 23 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index 7c2ed6eae53a..bd4b37f46f41 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -314,6 +314,17 @@ static void pci_epf_test_print_rate(struct pci_epf_test *epf_test,
>  		 (u64)ts.tv_sec, (u32)ts.tv_nsec, rate);
>  }
>  
> +static int pci_epf_test_check_dma(struct pci_epf_test *epf_test,
> +				   struct pci_epf_test_reg *reg)
> +{
> +	if ((READ_ONCE(reg->flags) & FLAG_USE_DMA) &&
> +	    !epf_test->dma_supported) {
> +		dev_err(&epf_test->epf->dev, "Cannot transfer data using DMA\n");

While at it, can we change this message to be clear, e.g. "DMA not supported".
"Cannot ..." is vague and does not state the reason why it cannot be done :)

> +		return -EIO;
> +	}
> +	return 0;
> +}
> +
>  static void pci_epf_test_copy(struct pci_epf_test *epf_test,
>  			      struct pci_epf_test_reg *reg)
>  {
> @@ -327,6 +338,10 @@ static void pci_epf_test_copy(struct pci_epf_test *epf_test,
>  	struct device *dev = &epf->dev;
>  	struct pci_epc *epc = epf->epc;
>  
> +	ret = pci_epf_test_check_dma(epf_test, reg);
> +	if (ret)
> +		goto err;
> +
>  	src_addr = pci_epc_mem_alloc_addr(epc, &src_phys_addr, reg->size);
>  	if (!src_addr) {
>  		dev_err(dev, "Failed to allocate source address\n");
> @@ -423,6 +438,10 @@ static void pci_epf_test_read(struct pci_epf_test *epf_test,
>  	struct pci_epc *epc = epf->epc;
>  	struct device *dma_dev = epf->epc->dev.parent;
>  
> +	ret = pci_epf_test_check_dma(epf_test, reg);
> +	if (ret)
> +		goto err;
> +
>  	src_addr = pci_epc_mem_alloc_addr(epc, &phys_addr, reg->size);
>  	if (!src_addr) {
>  		dev_err(dev, "Failed to allocate address\n");
> @@ -507,6 +526,10 @@ static void pci_epf_test_write(struct pci_epf_test *epf_test,
>  	struct pci_epc *epc = epf->epc;
>  	struct device *dma_dev = epf->epc->dev.parent;
>  
> +	ret = pci_epf_test_check_dma(epf_test, reg);
> +	if (ret)
> +		goto err;
> +
>  	dst_addr = pci_epc_mem_alloc_addr(epc, &phys_addr, reg->size);
>  	if (!dst_addr) {
>  		dev_err(dev, "Failed to allocate address\n");
> @@ -647,12 +670,6 @@ static void pci_epf_test_cmd_handler(struct work_struct *work)
>  	WRITE_ONCE(reg->command, 0);
>  	WRITE_ONCE(reg->status, 0);
>  
> -	if ((READ_ONCE(reg->flags) & FLAG_USE_DMA) &&
> -	    !epf_test->dma_supported) {
> -		dev_err(dev, "Cannot transfer data using DMA\n");
> -		goto reset_handler;
> -	}
> -
>  	if (reg->irq_type > IRQ_TYPE_MSIX) {
>  		dev_err(dev, "Failed to detect IRQ type\n");
>  		goto reset_handler;

-- 
Damien Le Moal
Western Digital Research