Re: [PATCH v3] cx23885: only reset DMA on problematic CPUs

[Mauro Carvalho Chehab <mchehab@kernel.org>]

Em Wed, 19 Dec 2018 11:07:01 -0600
Brad Love <brad@nextdimension.cc> escreveu:

> It is reported that commit 95f408bbc4e4 ("media: cx23885: Ryzen DMA
> related RiSC engine stall fixes") caused regresssions with other CPUs.
> 
> Ensure that the quirk will be applied only for the CPUs that
> are known to cause problems.
> 
> A module option is added for explicit control of the behaviour.
> 
> Fixes: 95f408bbc4e4 ("media: cx23885: Ryzen DMA related RiSC engine stall fixes")
> 
> Signed-off-by: Brad Love <brad@nextdimension.cc>

Thanks!

Patch applied and sent upstream.

Regards,
Mauro

> ---
> Since v2:
> - Replaced sizeof with ARRAY_SIZE
> - Fixed column 80 checkpatch complaint
> Changes since v1:
> - Added module option for three way control
> - Removed '7' from pci id description, Ryzen 3 is the same id
> 
>  drivers/media/pci/cx23885/cx23885-core.c | 55 ++++++++++++++++++++++++++++++--
>  drivers/media/pci/cx23885/cx23885.h      |  2 ++
>  2 files changed, 55 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/pci/cx23885/cx23885-core.c b/drivers/media/pci/cx23885/cx23885-core.c
> index 39804d8..e2e3649 100644
> --- a/drivers/media/pci/cx23885/cx23885-core.c
> +++ b/drivers/media/pci/cx23885/cx23885-core.c
> @@ -23,6 +23,7 @@
>  #include <linux/moduleparam.h>
>  #include <linux/kmod.h>
>  #include <linux/kernel.h>
> +#include <linux/pci.h>
>  #include <linux/slab.h>
>  #include <linux/interrupt.h>
>  #include <linux/delay.h>
> @@ -41,6 +42,18 @@ MODULE_AUTHOR("Steven Toth <stoth@linuxtv.org>");
>  MODULE_LICENSE("GPL");
>  MODULE_VERSION(CX23885_VERSION);
>  
> +/*
> + * Some platforms have been found to require periodic resetting of the DMA
> + * engine. Ryzen and XEON platforms are known to be affected. The symptom
> + * encountered is "mpeg risc op code error". Only Ryzen platforms employ
> + * this workaround if the option equals 1. The workaround can be explicitly
> + * disabled for all platforms by setting to 0, the workaround can be forced
> + * on for any platform by setting to 2.
> + */
> +static unsigned int dma_reset_workaround = 1;
> +module_param(dma_reset_workaround, int, 0644);
> +MODULE_PARM_DESC(dma_reset_workaround, "periodic RiSC dma engine reset; 0-force disable, 1-driver detect (default), 2-force enable");
> +
>  static unsigned int debug;
>  module_param(debug, int, 0644);
>  MODULE_PARM_DESC(debug, "enable debug messages");
> @@ -603,8 +616,13 @@ static void cx23885_risc_disasm(struct cx23885_tsport *port,
>  
>  static void cx23885_clear_bridge_error(struct cx23885_dev *dev)
>  {
> -	uint32_t reg1_val = cx_read(TC_REQ); /* read-only */
> -	uint32_t reg2_val = cx_read(TC_REQ_SET);
> +	uint32_t reg1_val, reg2_val;
> +
> +	if (!dev->need_dma_reset)
> +		return;
> +
> +	reg1_val = cx_read(TC_REQ); /* read-only */
> +	reg2_val = cx_read(TC_REQ_SET);
>  
>  	if (reg1_val && reg2_val) {
>  		cx_write(TC_REQ, reg1_val);
> @@ -2058,6 +2076,37 @@ void cx23885_gpio_enable(struct cx23885_dev *dev, u32 mask, int asoutput)
>  	/* TODO: 23-19 */
>  }
>  
> +static struct {
> +	int vendor, dev;
> +} const broken_dev_id[] = {
> +	/* According with
> +	 * https://openbenchmarking.org/system/1703021-RI-AMDZEN08075/Ryzen%207%201800X/lspci,
> +	 * 0x1451 is PCI ID for the IOMMU found on Ryzen
> +	 */
> +	{ PCI_VENDOR_ID_AMD, 0x1451 },
> +};
> +
> +static bool cx23885_does_need_dma_reset(void)
> +{
> +	int i;
> +	struct pci_dev *pdev = NULL;
> +
> +	if (dma_reset_workaround == 0)
> +		return false;
> +	else if (dma_reset_workaround == 2)
> +		return true;
> +
> +	for (i = 0; i < ARRAY_SIZE(broken_dev_id); i++) {
> +		pdev = pci_get_device(broken_dev_id[i].vendor,
> +					broken_dev_id[i].dev, NULL);
> +		if (pdev) {
> +			pci_dev_put(pdev);
> +			return true;
> +		}
> +	}
> +	return false;
> +}
> +
>  static int cx23885_initdev(struct pci_dev *pci_dev,
>  			   const struct pci_device_id *pci_id)
>  {
> @@ -2069,6 +2118,8 @@ static int cx23885_initdev(struct pci_dev *pci_dev,
>  	if (NULL == dev)
>  		return -ENOMEM;
>  
> +	dev->need_dma_reset = cx23885_does_need_dma_reset();
> +
>  	err = v4l2_device_register(&pci_dev->dev, &dev->v4l2_dev);
>  	if (err < 0)
>  		goto fail_free;
> diff --git a/drivers/media/pci/cx23885/cx23885.h b/drivers/media/pci/cx23885/cx23885.h
> index d54c7ee..cf965ef 100644
> --- a/drivers/media/pci/cx23885/cx23885.h
> +++ b/drivers/media/pci/cx23885/cx23885.h
> @@ -451,6 +451,8 @@ struct cx23885_dev {
>  	/* Analog raw audio */
>  	struct cx23885_audio_dev   *audio_dev;
>  
> +	/* Does the system require periodic DMA resets? */
> +	unsigned int		need_dma_reset:1;
>  };
>  
>  static inline struct cx23885_dev *to_cx23885(struct v4l2_device *v4l2_dev)



Thanks,
Mauro