Re: [PATCH 1/2] hwmon: (ads7871) Add mutex to serialize SPI transactions

[Tabrez Ahmed <tabreztalks@gmail.com>]

On 3/29/26 08:46, Guenter Roeck wrote:
> When using the with_info API to register the hwmon device, the subsystem 
> already
> serializes sysfs accesses. The next patch converts the driver to use the
> with_info API. Pleas explain why the extra protection is necessary.

Ah yes. I originally wrote the mutex patch to fix the race condition in 
the legacy sysfs code, but totally missed that migrating to with_info 
handles the serialization for us natively.

> Sashiko has the same feedback:
> 
> https://sashiko.dev/#/patchset/20260328182015.220298-1- 
> tabreztalks%40gmail.com

Separately, Sashiko flagged a pre-existing bug where 
ads7871_write_reg8() passes a stack-allocated array (u8 tmp[2]) to 
spi_write(), breaking DMA.

To fix this properly, I need to move the buffer into the device's 
private data structure. However, doing so requires serialization to 
prevent concurrent reads from corrupting the shared buffer. Since moving 
to with_info provides that serialization, my plan for the v2 series is:

- Patch 1: Convert to hwmon_device_register_with_info (which natively 
serializes the driver).
- Patch 2: Fix the SPI DMA bug by introducing a shared tx_buf (now 
safely protected by the hwmon core).

I will drop the custom mutex entirely and send out v2 with this structure.

Thanks,
Tabrez