Re: [PATCH v4 6/9] bus: mhi: Load DDR training data using per-device serial number

[Jeff Hugo <jeff.hugo@oss.qualcomm.com>]

On 3/19/2026 12:31 AM, Kishore Batta wrote:
> Devices may provide device-specific DDR training data that can be reused
> across boot to avoid retraining and reduce boot time. The Sahara driver
> currently always falls back to the default DDR training image, even when
> per-device training data is available.
> 
> Extend the firmware loading logic to first attempt loading a per-device
> DDR training image using the device serial number. If the serial-specific
> image is not present, fallback to the existing default image, preserving
> current behavior.
> 
> This change enables DDR training data reuse when available while keeping
> the existing training flow unchanged for devices without saved data.
> 
> Signed-off-by: Kishore Batta <kishore.batta@oss.qualcomm.com>
> ---
>   drivers/bus/mhi/sahara/sahara.c | 47 ++++++++++++++++++++++++++++++++---------
>   1 file changed, 37 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/bus/mhi/sahara/sahara.c b/drivers/bus/mhi/sahara/sahara.c
> index 4ea14c57774f51a778289d7409372a6ab21fea60..0a0f578aaa47ab2c4ca0765666b392fb9936ddd5 100644
> --- a/drivers/bus/mhi/sahara/sahara.c
> +++ b/drivers/bus/mhi/sahara/sahara.c
> @@ -61,6 +61,8 @@
>   #define SAHARA_MEM_DEBUG64_LENGTH	0x18
>   #define SAHARA_MEM_READ64_LENGTH	0x18
>   
> +#define SAHARA_DDR_TRAINING_IMG_ID	34
> +
>   struct sahara_packet {
>   	__le32 cmd;
>   	__le32 length;
> @@ -365,16 +367,41 @@ static int sahara_find_image(struct sahara_context *context, u32 image_id)
>   		return 0;
>   	}
>   
> -	/*
> -	 * This image might be optional. The device may continue without it.
> -	 * Only the device knows. Suppress error messages that could suggest an
> -	 * a problem when we were actually able to continue.
> -	 */
> -	ret = sahara_request_fw(context, context->image_table[image_id]);
> -	if (ret) {
> -		dev_dbg(&context->mhi_dev->dev, "request for image id %d / file %s failed %d\n",
> -			image_id, context->image_table[image_id], ret);
> -		return ret;
> +	/* DDR training special case: Try per-serial number file first */
> +	if (image_id == SAHARA_DDR_TRAINING_IMG_ID && context->fw_folder) {
> +		u32 serial_num = context->mhi_dev->mhi_cntrl->serial_number;
> +
> +		fw_path = kasprintf(GFP_KERNEL,
> +				    "qcom/%s/mdmddr_0x%x.mbn",
> +				    context->fw_folder, serial_num);
> +		if (!fw_path)
> +			return -ENOMEM;
> +
> +		ret = sahara_request_fw(context, fw_path);
> +		kfree(fw_path);
> +
> +		if (ret) {
> +			ret = sahara_request_fw(context, context->image_table[image_id]);
> +			if (ret) {
> +				dev_dbg(&context->mhi_dev->dev,
> +					"request for image id %d / file %s failed %d\n",
> +					image_id, context->image_table[image_id], ret);
> +			}
> +			return ret;
> +		}

This is entirely redundant with the else in the next line. I don't 
understand why id 34 could be reserved for training data, but also be a 
valid image if the training data was not found.

Just have the if that looks for the training data, and an if that if 
there is no found image, do a normal lookup.

> +	} else {
> +		/*
> +		 * This image might be optional. The device may continue without it.
> +		 * Only the device knows. Suppress error messages that could suggest an
> +		 * a problem when we were actually able to continue.
> +		 */
> +		ret = sahara_request_fw(context, context->image_table[image_id]);
> +		if (ret) {
> +			dev_dbg(&context->mhi_dev->dev,
> +				"request for image id %d / file %s failed %d\n",
> +				image_id, context->image_table[image_id], ret);
> +			return ret;
> +		}
>   	}
>   
>   	context->active_image_id = image_id;
>