Re: [PATCH] [media] af9035: fix for MXL5007T devices with I2C read issues

[Antti Palosaari <crope@iki.fi>]

Hello
I am not happy with that new module parameter as I cannot see real need 
for it. So get rid of it.

Better to compare both VID and PID when enabling that work-around. 
Driver supports currently quite many different USB IDs and there is 
still small risk duplicate PID will exists at some point enabling 
work-around for wrong device.

regards
Antti



On 04/15/2016 06:37 PM, Alessandro Radicati wrote:
> The MXL5007T tuner will lock-up on some devices after an I2C read
> transaction.  This patch adds a kernel module parameter "no_read" to work
> around this issue by inhibiting such operations and emulating a 0x00
> response.  The workaround is applied automatically to USB product IDs known
> to exhibit this flaw, unless the kernel module parameter is specified.
>
> Signed-off-by: Alessandro Radicati <alessandro@radicati.net>
> ---
>   drivers/media/usb/dvb-usb-v2/af9035.c | 27 +++++++++++++++++++++++++++
>   drivers/media/usb/dvb-usb-v2/af9035.h |  1 +
>   2 files changed, 28 insertions(+)
>
> diff --git a/drivers/media/usb/dvb-usb-v2/af9035.c b/drivers/media/usb/dvb-usb-v2/af9035.c
> index 2638e32..8225403 100644
> --- a/drivers/media/usb/dvb-usb-v2/af9035.c
> +++ b/drivers/media/usb/dvb-usb-v2/af9035.c
> @@ -24,6 +24,10 @@
>   /* Max transfer size done by I2C transfer functions */
>   #define MAX_XFER_SIZE  64
>
> +static int dvb_usb_af9035_no_read = -1;
> +module_param_named(no_read, dvb_usb_af9035_no_read, int, 0644);
> +MODULE_PARM_DESC(no_read, "Emulate I2C reads for devices that do not support them.");
> +
>   DVB_DEFINE_MOD_OPT_ADAPTER_NR(adapter_nr);
>
>   static u16 af9035_checksum(const u8 *buf, size_t len)
> @@ -348,6 +352,9 @@ static int af9035_i2c_master_xfer(struct i2c_adapter *adap,
>
>   			ret = af9035_rd_regs(d, reg, &msg[1].buf[0],
>   					msg[1].len);
> +		} else if (state->no_read) {
> +			memset(msg[1].buf, 0, msg[1].len);
> +			ret = 0;
>   		} else {
>   			/* I2C write + read */
>   			u8 buf[MAX_XFER_SIZE];
> @@ -421,6 +428,9 @@ static int af9035_i2c_master_xfer(struct i2c_adapter *adap,
>   		if (msg[0].len > 40) {
>   			/* TODO: correct limits > 40 */
>   			ret = -EOPNOTSUPP;
> +		} else if (state->no_read) {
> +			memset(msg[0].buf, 0, msg[0].len);
> +			ret = 0;
>   		} else {
>   			/* I2C read */
>   			u8 buf[5];
> @@ -962,6 +972,23 @@ skip_eeprom:
>   			state->af9033_config[i].clock = clock_lut_af9035[tmp];
>   	}
>
> +	/* Some MXL5007T devices cannot properly handle tuner I2C read ops. */
> +	if (dvb_usb_af9035_no_read != -1) { /* Override with module param */
> +		state->no_read = dvb_usb_af9035_no_read == 0 ? false : true;
> +	} else {
> +		switch (le16_to_cpu(d->udev->descriptor.idProduct)) {
> +		case USB_PID_AVERMEDIA_A867:
> +		case USB_PID_AVERMEDIA_TWINSTAR:
> +			dev_info(&d->udev->dev,
> +				"%s: Device may have issues with I2C read operations. Enabling fix.\n",
> +				KBUILD_MODNAME);
> +			state->no_read = true;
> +			break;
> +		default:
> +			state->no_read = false;
> +		}
> +	}
> +
>   	return 0;
>
>   err:
> diff --git a/drivers/media/usb/dvb-usb-v2/af9035.h b/drivers/media/usb/dvb-usb-v2/af9035.h
> index df22001..a76dafa 100644
> --- a/drivers/media/usb/dvb-usb-v2/af9035.h
> +++ b/drivers/media/usb/dvb-usb-v2/af9035.h
> @@ -62,6 +62,7 @@ struct state {
>   	u8 chip_version;
>   	u16 chip_type;
>   	u8 dual_mode:1;
> +	u8 no_read:1;
>   	u16 eeprom_addr;
>   	u8 af9033_i2c_addr[2];
>   	struct af9033_config af9033_config[2];
>

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