t113-i mipi屏幕，longan系统屏幕的mapping->base为0是什么原因？具体是在哪里分配的呢，是不是需要在menuconfig里面打开某些配置？请大佬指教
static int __iommu_map_sg(struct device *dev, struct scatterlist *sg, int nents,
enum dma_data_direction dir, unsigned long attrs,
bool is_coherent)
{
printk("[damon_mapping]{__iommu_map_sg} mapping->base 0x%px\n", dev->archdata.mapping->base);
struct scatterlist *s = sg, *dma = sg, *start = sg;
int i, count = 0;
unsigned int offset = s->offset;
unsigned int size = s->offset + s->length;
unsigned int max = dma_get_max_seg_size(dev);
for (i = 1; i < nents; i++) {
s = sg_next(s);
s->dma_address = DMA_MAPPING_ERROR;
s->dma_length = 0;
if (s->offset || (size & ~PAGE_MASK) || size + s->length > max) {
if (__map_sg_chunk(dev, start, size, &dma->dma_address,
dir, attrs, is_coherent) < 0){
goto bad_mapping;}
dma->dma_address += offset;
dma->dma_length = size - offset;
size = offset = s->offset;
start = s;
dma = sg_next(dma);
count += 1;
}
size += s->length;
}
if (__map_sg_chunk(dev, start, size, &dma->dma_address, dir, attrs,
is_coherent) < 0){
goto bad_mapping;}
dma->dma_address += offset;
dma->dma_length = size - offset;
return count+1;
bad_mapping:
for_each_sg(sg, s, count, i)
__iommu_remove_mapping(dev, sg_dma_address(s), sg_dma_len(s));
return 0;
}