Re: [PATCH v4 5/6] pds_fwctl: add rpc and query support

["Nelson, Shannon" <shannon.nelson@amd.com>]

On 3/21/2025 7:33 AM, Dan Carpenter wrote:
> On Wed, Mar 19, 2025 at 02:32:36PM -0700, Shannon Nelson wrote:
>> +static struct pds_fwctl_query_data *pdsfc_get_endpoints(struct pdsfc_dev *pdsfc,
>> +                                                     dma_addr_t *pa)
>> +{
>> +     struct device *dev = &pdsfc->fwctl.dev;
>> +     union pds_core_adminq_comp comp = {0};
>> +     struct pds_fwctl_query_data *data;
>> +     union pds_core_adminq_cmd cmd;
>> +     dma_addr_t data_pa;
>> +     int err;
>> +
>> +     data = dma_alloc_coherent(dev->parent, PAGE_SIZE, &data_pa, GFP_KERNEL);
>> +     err = dma_mapping_error(dev, data_pa);
>> +     if (err) {
>> +             dev_err(dev, "Failed to map endpoint list\n");
>> +             return ERR_PTR(err);
>> +     }
> 
> This doesn't work.  The dma_alloc_coherent() function doesn't necessarily
> initialize data_pa.  I don't know very much about DMA but can't we just
> check:
> 
>          data = dma_alloc_coherent(dev->parent, PAGE_SIZE, &data_pa, GFP_KERNEL);
>          if (!data)
>                  return ERR_PTR(-ENOMEM);
> 
> regards,
> dan carpenter
> 

Yes, you are right.  This works for the dma_map_single() calls on 
already allocated blocks, but not here for the alloc-and-map calls.  I 
think something like this would be better:


Author: Shannon Nelson <shannon.nelson@amd.com>
Date:   Fri Mar 21 09:37:52 2025 -0700

     pds_fwctl: fix use of dma_mapping_error()

     The dma_alloc_coherent() call only returns NULL if there is an
     error, so checking the dma_handle with dma_mapping_error() is
     not useful.  Fix this by checking the returned address for NULL.

     Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>

diff --git a/drivers/fwctl/pds/main.c b/drivers/fwctl/pds/main.c
index 6fedde2a962e..e50e1bbdff9a 100644
--- a/drivers/fwctl/pds/main.c
+++ b/drivers/fwctl/pds/main.c
@@ -76,8 +76,7 @@ static int pdsfc_identify(struct pdsfc_dev *pdsfc)
         int err;

         ident = dma_alloc_coherent(dev->parent, sizeof(*ident), 
&ident_pa, GFP_KERNEL);
-       err = dma_mapping_error(dev->parent, ident_pa);
-       if (err) {
+       if (!ident) {
                 dev_err(dev, "Failed to map ident buffer\n");
                 return err;
         }
@@ -151,8 +150,7 @@ static struct pds_fwctl_query_data 
*pdsfc_get_endpoints(struct pdsfc_dev *pdsfc,
         int err;

         data = dma_alloc_coherent(dev->parent, PAGE_SIZE, &data_pa, 
GFP_KERNEL);
-       err = dma_mapping_error(dev, data_pa);
-       if (err) {
+       if (!data) {
                 dev_err(dev, "Failed to map endpoint list\n");
                 return ERR_PTR(err);
         }
@@ -221,8 +219,7 @@ static struct pds_fwctl_query_data 
*pdsfc_get_operations(struct pdsfc_dev *pdsfc

         /* Query the operations list for the given endpoint */
         data = dma_alloc_coherent(dev->parent, PAGE_SIZE, &data_pa, 
GFP_KERNEL);
-       err = dma_mapping_error(dev->parent, data_pa);
-       if (err) {
+       if (!data) {
                 dev_err(dev, "Failed to map operations list\n");
                 return ERR_PTR(err);
         }