Re: [PATCH v2 1/3] platform/x86: intel_scu_ipc: Replace workaround by 32-bit IO

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Mon, 21 Oct 2024, Andy Shevchenko wrote:

> The theory is that the so called workaround in pwr_reg_rdwr() is
> the actual reader of the data in 32-bit chunks. For some reason
> the 8-bit IO won't fail after that. Replace the workaround by using
> 32-bit IO explicitly and then memcpy() as much data as was requested
> by the user. The same approach is already in use in
> intel_scu_ipc_dev_command_with_size().
>
> Tested-by: Ferry Toth <fntoth@gmail.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/platform/x86/intel_scu_ipc.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/platform/x86/intel_scu_ipc.c b/drivers/platform/x86/intel_scu_ipc.c
> index 5b16d29c93d7..290b38627542 100644
> --- a/drivers/platform/x86/intel_scu_ipc.c
> +++ b/drivers/platform/x86/intel_scu_ipc.c
> @@ -217,12 +217,6 @@ static inline u8 ipc_read_status(struct intel_scu_ipc_dev *scu)
>  	return __raw_readl(scu->ipc_base + IPC_STATUS);
>  }
>  
> -/* Read ipc byte data */
> -static inline u8 ipc_data_readb(struct intel_scu_ipc_dev *scu, u32 offset)
> -{
> -	return readb(scu->ipc_base + IPC_READ_BUFFER + offset);
> -}
> -
>  /* Read ipc u32 data */
>  static inline u32 ipc_data_readl(struct intel_scu_ipc_dev *scu, u32 offset)
>  {
> @@ -325,11 +319,10 @@ static int pwr_reg_rdwr(struct intel_scu_ipc_dev *scu, u16 *addr, u8 *data,
>  	}
>  
>  	err = intel_scu_ipc_check_status(scu);
> -	if (!err && id == IPC_CMD_PCNTRL_R) { /* Read rbuf */
> -		/* Workaround: values are read as 0 without memcpy_fromio */
> -		memcpy_fromio(cbuf, scu->ipc_base + 0x90, 16);
> -		for (nc = 0; nc < count; nc++)
> -			data[nc] = ipc_data_readb(scu, nc);
> +	if (!err) { /* Read rbuf */

What is the reason for the removal of that id check? This seems a clear 
logic change but why? And if you remove want to remove that check, what 
that comment then means?

> +		for (nc = 0, offset = 0; nc < 4; nc++, offset += 4)
> +			wbuf[nc] = ipc_data_readl(scu, offset);
> +		memcpy(data, wbuf, count);

So do we actually need to read more than
DIV_ROUND_UP(min(count, 16U), sizeof(u32))? Because that's the approach 
used in intel_scu_ipc_dev_command_with_size() which you referred to.

>  	}
>  	mutex_unlock(&ipclock);
>  	return err;

FYI (unrelated to this patch), there seems to be some open-coded 
FIELD_PREP()s in pwr_reg_rdwr(), some of which is common code between 
those if branches too.

-- 
 i.