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mmc: bcm2835: DMA mapping improvements

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As pointed out by sashiko bot in [0], recent proposed changes to
dma_max_mapping_size() may affect the driver.

While the issue reported may be a false positive, Robin pointed out some
other DMA-related issues in the driver which are addressed here:
- the DMA max mapping size is irrelevant for the programmed IO mode of
  operation
- we should not call dma_max_mapping_size() on the MMC host platform
  device, but rather the DMA engine device

In addition, it's better to use the device returned from
dmaengine_get_dma_device() for dma_umap_sg() and dma_unmap_sg(), and not
reference the DMA channel device directly.

[0] https://lore.kernel.org/linux-scsi/d82926fe-4557-401d-ae58-4302fef5657c@oracle.com/#t

Signed-off-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Ulf Hansson <ulfh@kernel.org>
This commit is contained in:
John Garry 2026-07-14 08:44:56 +00:00 committed by Ulf Hansson
parent cf93175e7e
commit 5608386899
1 changed files with 19 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
drivers/mmc/host/bcm2835.c
View File

@ -188,7 +188,7 @@ struct bcm2835_host {
u32 drain_words;
struct page *drain_page;
u32 drain_offset;
bool use_dma;
struct device *dma_dev;
};
static void bcm2835_dumpcmd(struct bcm2835_host *host, struct mmc_command *cmd,
@ -494,8 +494,7 @@ void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
&host->dma_cfg_rx :
&host->dma_cfg_tx);
sg_len = dma_map_sg(dma_chan->device->dev, data->sg, data->sg_len,
dir_data);
sg_len = dma_map_sg(host->dma_dev, data->sg, data->sg_len, dir_data);
if (!sg_len)
return;
@ -503,8 +502,7 @@ void bcm2835_prepare_dma(struct bcm2835_host *host, struct mmc_data *data)
DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
if (!desc) {
dma_unmap_sg(dma_chan->device->dev, data->sg, data->sg_len,
dir_data);
dma_unmap_sg(host->dma_dev, data->sg, data->sg_len, dir_data);
return;
}
@ -1057,7 +1055,7 @@ static void bcm2835_dma_complete_work(struct work_struct *work)
data = host->data;
if (host->dma_chan) {
dma_unmap_sg(host->dma_chan->device->dev,
dma_unmap_sg(host->dma_dev,
data->sg, data->sg_len,
host->dma_dir);
@ -1201,7 +1199,7 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
return;
}
if (host->use_dma && mrq->data && (mrq->data->blocks > PIO_THRESHOLD))
if (host->dma_dev && mrq->data && (mrq->data->blocks > PIO_THRESHOLD))
bcm2835_prepare_dma(host, mrq->data);
host->use_sbc = !!mrq->sbc && host->mrq->data &&
@ -1281,10 +1279,7 @@ static int bcm2835_add_host(struct bcm2835_host *host)
if (!host->dma_chan_rxtx) {
dev_warn(dev, "unable to initialise DMA channel. Falling back to PIO\n");
host->use_dma = false;
} else {
host->use_dma = true;
host->dma_cfg_tx.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
host->dma_cfg_tx.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
host->dma_cfg_tx.direction = DMA_MEM_TO_DEV;
@ -1297,15 +1292,21 @@ static int bcm2835_add_host(struct bcm2835_host *host)
host->dma_cfg_rx.src_addr = host->phys_addr + SDDATA;
host->dma_cfg_rx.dst_addr = 0;
if (dmaengine_slave_config(host->dma_chan_rxtx,
&host->dma_cfg_tx) != 0 ||
dmaengine_slave_config(host->dma_chan_rxtx,
&host->dma_cfg_rx) != 0)
host->use_dma = false;
if (!dmaengine_slave_config(host->dma_chan_rxtx,
&host->dma_cfg_tx) &&
!dmaengine_slave_config(host->dma_chan_rxtx,
&host->dma_cfg_rx)) {
host->dma_dev =
dmaengine_get_dma_device(host->dma_chan_rxtx);
}
}
mmc->max_segs = 128;
mmc->max_req_size = min_t(size_t, 524288, dma_max_mapping_size(dev));
mmc->max_req_size = 524288;
if (host->dma_dev) {
mmc->max_req_size = min_t(size_t, mmc->max_req_size,
dma_max_mapping_size(host->dma_dev));
}
mmc->max_seg_size = mmc->max_req_size;
mmc->max_blk_size = 1024;
mmc->max_blk_count = 65535;
@ -1336,10 +1337,10 @@ static int bcm2835_add_host(struct bcm2835_host *host)
}
pio_limit_string[0] = '\0';
if (host->use_dma && (PIO_THRESHOLD > 0))
if (host->dma_dev && (PIO_THRESHOLD > 0))
sprintf(pio_limit_string, " (>%d)", PIO_THRESHOLD);
dev_info(dev, "loaded - DMA %s%s\n",
host->use_dma ? "enabled" : "disabled", pio_limit_string);
host->dma_dev ? "enabled" : "disabled", pio_limit_string);
return 0;
}