Re: [RFC PATCH] i2c: imx: dma map the i2c data i/o register

[Laurentiu Tudor <laurentiu.tudor@nxp.com>]

Hi Robin,

On 16.01.2019 19:55, Robin Murphy wrote:
> On 16/01/2019 16:17, Laurentiu Tudor wrote:
>> This is an attempt to fix an iommu exception when doing dma to the
>> i2c controller with EDMA. Without these mappings the smmu raises a
>> context fault [1] exactly with the address of the i2c data i/o reg.
>> This was seen on an NXP LS1043A chip while working on enabling SMMU.
> 
> Rather than gradually adding much the same code to potentially every 
> possible client driver, can it not be implemented once in the edma 
> driver as was done for pl330 and rcar-dmac? That also sidesteps any of 
> the nastiness of smuggling a dma_addr_t via a phys_addr_t variable.

Thanks for the pointer. I was actually unsure where this should be 
tackled: either i2c or dma side. Plus I somehow managed to completely 
miss the support added in the dma drivers you mention. I'll start 
looking into stealing some of your code [1]. :-)

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4d6d74e22096543cb3b35e717cf1b9aea3655f37

---
Best Regards, Laurentiu


> 
>> [1] arm-smmu 9000000.iommu: Unhandled context fault: fsr=0x402,
>>      iova=0x02180004, fsynr=0x150021, cb=7
>>
>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
>> ---
>>   drivers/i2c/busses/i2c-imx.c | 57 +++++++++++++++++++++++++++++-------
>>   1 file changed, 47 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
>> index 4e34b1572756..07cc8f4b45b9 100644
>> --- a/drivers/i2c/busses/i2c-imx.c
>> +++ b/drivers/i2c/busses/i2c-imx.c
>> @@ -202,6 +202,9 @@ struct imx_i2c_struct {
>>       struct pinctrl_state *pinctrl_pins_gpio;
>>       struct imx_i2c_dma    *dma;
>> +
>> +    dma_addr_t        dma_tx_addr;
>> +    dma_addr_t        dma_rx_addr;
>>   };
>>   static const struct imx_i2c_hwdata imx1_i2c_hwdata = {
>> @@ -274,17 +277,20 @@ static inline unsigned char 
>> imx_i2c_read_reg(struct imx_i2c_struct *i2c_imx,
>>   /* Functions for DMA support */
>>   static int i2c_imx_dma_request(struct imx_i2c_struct *i2c_imx,
>> -                   dma_addr_t phy_addr)
>> +                   phys_addr_t phy_addr)
>>   {
>>       struct imx_i2c_dma *dma;
>>       struct dma_slave_config dma_sconfig;
>>       struct device *dev = &i2c_imx->adapter.dev;
>>       int ret;
>> +    phys_addr_t i2dr_pa;
>>       dma = devm_kzalloc(dev, sizeof(*dma), GFP_KERNEL);
>>       if (!dma)
>>           return -ENOMEM;
>> +    i2dr_pa = phy_addr + (IMX_I2C_I2DR << i2c_imx->hwdata->regshift);
>> +
>>       dma->chan_tx = dma_request_chan(dev, "tx");
>>       if (IS_ERR(dma->chan_tx)) {
>>           ret = PTR_ERR(dma->chan_tx);
>> @@ -293,15 +299,25 @@ static int i2c_imx_dma_request(struct 
>> imx_i2c_struct *i2c_imx,
>>           goto fail_al;
>>       }
>> -    dma_sconfig.dst_addr = phy_addr +
>> -                (IMX_I2C_I2DR << i2c_imx->hwdata->regshift);
>> +    i2c_imx->dma_tx_addr = dma_map_resource(dma->chan_tx->device->dev,
>> +                        i2dr_pa,
>> +                        DMA_SLAVE_BUSWIDTH_1_BYTE,
>> +                        DMA_MEM_TO_DEV, 0);
>> +    ret = dma_mapping_error(dma->chan_tx->device->dev,
>> +                i2c_imx->dma_tx_addr);
>> +    if (ret) {
>> +        dev_err(dev, "can't dma map tx destination (%d)\n", ret);
>> +        goto fail_tx;
>> +    }
>> +
>> +    dma_sconfig.dst_addr = i2c_imx->dma_tx_addr;
>>       dma_sconfig.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
>>       dma_sconfig.dst_maxburst = 1;
>>       dma_sconfig.direction = DMA_MEM_TO_DEV;
>>       ret = dmaengine_slave_config(dma->chan_tx, &dma_sconfig);
>>       if (ret < 0) {
>>           dev_err(dev, "can't configure tx channel (%d)\n", ret);
>> -        goto fail_tx;
>> +        goto fail_tx_dma;
>>       }
>>       dma->chan_rx = dma_request_chan(dev, "rx");
>> @@ -309,18 +325,28 @@ static int i2c_imx_dma_request(struct 
>> imx_i2c_struct *i2c_imx,
>>           ret = PTR_ERR(dma->chan_rx);
>>           if (ret != -ENODEV && ret != -EPROBE_DEFER)
>>               dev_err(dev, "can't request DMA rx channel (%d)\n", ret);
>> -        goto fail_tx;
>> +        goto fail_tx_dma;
>>       }
>> -    dma_sconfig.src_addr = phy_addr +
>> -                (IMX_I2C_I2DR << i2c_imx->hwdata->regshift);
>> +    i2c_imx->dma_rx_addr = dma_map_resource(dma->chan_rx->device->dev,
>> +                        i2dr_pa,
>> +                        DMA_SLAVE_BUSWIDTH_1_BYTE,
>> +                        DMA_DEV_TO_MEM, 0);
>> +    ret = dma_mapping_error(dma->chan_rx->device->dev,
>> +                i2c_imx->dma_rx_addr);
>> +    if (ret) {
>> +        dev_err(dev, "can't dma map rx source (%d)\n", ret);
>> +        goto fail_rx;
>> +    }
>> +
>> +    dma_sconfig.src_addr = i2c_imx->dma_rx_addr;
>>       dma_sconfig.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
>>       dma_sconfig.src_maxburst = 1;
>>       dma_sconfig.direction = DMA_DEV_TO_MEM;
>>       ret = dmaengine_slave_config(dma->chan_rx, &dma_sconfig);
>>       if (ret < 0) {
>>           dev_err(dev, "can't configure rx channel (%d)\n", ret);
>> -        goto fail_rx;
>> +        goto fail_rx_dma;
>>       }
>>       i2c_imx->dma = dma;
>> @@ -330,8 +356,14 @@ static int i2c_imx_dma_request(struct 
>> imx_i2c_struct *i2c_imx,
>>       return 0;
>> +fail_rx_dma:
>> +    dma_unmap_resource(dma->chan_rx->device->dev, i2c_imx->dma_rx_addr,
>> +               DMA_SLAVE_BUSWIDTH_1_BYTE, DMA_DEV_TO_MEM, 0);
>>   fail_rx:
>>       dma_release_channel(dma->chan_rx);
>> +fail_tx_dma:
>> +    dma_unmap_resource(dma->chan_tx->device->dev, i2c_imx->dma_tx_addr,
>> +               DMA_SLAVE_BUSWIDTH_1_BYTE, DMA_MEM_TO_DEV, 0);
>>   fail_tx:
>>       dma_release_channel(dma->chan_tx);
>>   fail_al:
>> @@ -1057,7 +1089,7 @@ static int i2c_imx_probe(struct platform_device 
>> *pdev)
>>       struct imxi2c_platform_data *pdata = dev_get_platdata(&pdev->dev);
>>       void __iomem *base;
>>       int irq, ret;
>> -    dma_addr_t phy_addr;
>> +    phys_addr_t phy_addr;
>>       dev_dbg(&pdev->dev, "<%s>\n", __func__);
>> @@ -1072,7 +1104,7 @@ static int i2c_imx_probe(struct platform_device 
>> *pdev)
>>       if (IS_ERR(base))
>>           return PTR_ERR(base);
>> -    phy_addr = (dma_addr_t)res->start;
>> +    phy_addr = res->start;
>>       i2c_imx = devm_kzalloc(&pdev->dev, sizeof(*i2c_imx), GFP_KERNEL);
>>       if (!i2c_imx)
>>           return -ENOMEM;
>> @@ -1220,6 +1252,11 @@ static int i2c_imx_remove(struct 
>> platform_device *pdev)
>>       pm_runtime_put_noidle(&pdev->dev);
>>       pm_runtime_disable(&pdev->dev);
>> +    dma_unmap_resource(&pdev->dev, i2c_imx->dma_tx_addr,
>> +               DMA_SLAVE_BUSWIDTH_1_BYTE, DMA_MEM_TO_DEV, 0);
>> +    dma_unmap_resource(&pdev->dev, i2c_imx->dma_rx_addr,
>> +               DMA_SLAVE_BUSWIDTH_1_BYTE, DMA_DEV_TO_MEM, 0);
>> +
>>       return 0;
>>   }
>>