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SubjectPatch?: Centralized DMA mapping in linux-2.5.6-pre2/drivers/scsi/scsi.c
	I have been exploring the daunting task of trying to port
the numerous scsi drivers in 2.5.6-pre2 that no longer build to
the DMA mapping interface described in Documentation/DMA-mapping.txt.
There are approximately 90 scsi host controller drivers in Linus's
tree. I believe that most of the effected drivers will need to
implement almost exactly the same code.

So, I have created the following patch which defines two
new flags that scsi host templates can set, which tell scsi.c to
handle mapping (and unmapping) or Scsi_Request.request_buffer and
Scsi_Request.sense_buffer, respectively (some drivers have no use
for mapping sense_buffer). All of the executable code is contained
in two static routines, scsi_map_dma and scsi_unmap_dma. So, the
patch should be pretty readable.

I believe this approach has the following advantages:

o less code to maintain
o faster cleanup of drivers/scsi
o saves a few bytes of system size if more than one
device driver
o drivers that do not use this facility should be unaffected,
o easier to make changes in the future, for example:
- scsi_map_dma could change all requests
that have use_sg=0 to one that have use_sg=1,
so drivers could eliminate the use_sg=0 case
before it becomes necessary to change all clients
to avoid use_sg=0.
- Perhaps DMA mapping could be moved out to
scsi_allocate_device and scsi_release_request,
so that it could be done a little less often.
- Perhaps allocate sense_buffer or request_buffer
via pci_pool_alloc, so it can be allocated from
high memory on systems that can DMA to it.

Here are some small disadvantages, and why this the change is worth it.

o Any driver that does not use named initializers for
its Scsi_Host_Template will break, but it's really unlikely
that such drivers have been maintained to reflect the
other 2.5 changes and not have named initializers.

o This change 20 bytes to Scsi_Request, but its a big
data structure to begin with and some of that
size can be made up if we can eliminate the use_sg=0
and, in many cases, the new variables are eliminating
the need to create the same variables in driver private
data.

o Right now, I only know that it compiles and links without
undefined symbols, but drivers that do not set the new
flags should not be affected.

Comments? Bugs in my implementation?

--
Adam J. Richter __ ______________ 4880 Stevens Creek Blvd, Suite 104
adam@yggdrasil.com \ / San Jose, California 95129-1034
+1 408 261-6630 | g g d r a s i l United States of America
fax +1 408 261-6631 "Free Software For The Rest Of Us."
--- linux-2.5.6-pre2/drivers/scsi/hosts.h Tue Feb 19 18:10:59 2002
+++ linux/drivers/scsi/hosts.h Wed Mar 6 01:10:44 2002
@@ -286,6 +286,11 @@

unsigned highmem_io:1;

+ /* Have the high level code automatically handle DMA mapping of
+ Scsi_Request->request_buffer and Scsi_Request->sense_buf. */
+ unsigned dma_map_request:1;
+ unsigned dma_map_sense:1;
+
/*
* Name of proc directory
*/
--- linux-2.5.6-pre2/drivers/scsi/scsi.h Tue Feb 19 18:10:58 2002
+++ linux/drivers/scsi/scsi.h Wed Mar 6 02:31:05 2002
@@ -734,12 +732,14 @@

struct timer_list eh_timeout; /* Used to time out the command. */
void *request_buffer; /* Actual requested buffer */
+ dma_addr_t request_dma_addr;

/* These elements define the operation we ultimately want to perform */
unsigned char data_cmnd[MAX_COMMAND_SIZE];
unsigned short old_use_sg; /* We save use_sg here when requesting
* sense info */
unsigned short use_sg; /* Number of pieces of scatter-gather */
+ unsigned short sgcnt_dma; /* Returned by pci_map_sg. */
unsigned short sglist_len; /* size of malloc'd scatter-gather list */
unsigned short abort_reason; /* If the mid-level code requests an
* abort, this is the reason. */
@@ -768,6 +768,7 @@
* when CHECK CONDITION is
* received on original command
* (auto-sense) */
+ dma_addr_t sense_dma_addr;

unsigned flags;

--- linux-2.5.6-pre2/drivers/scsi/scsi.c Tue Feb 19 18:11:03 2002
+++ linux/drivers/scsi/scsi.c Wed Mar 6 02:43:55 2002
@@ -309,6 +309,76 @@
return SRpnt;
}

+static inline void
+scsi_unmap_dma(Scsi_Cmnd *cmd)
+{
+ const Scsi_Host_Template *template = cmd->host->hostt;
+
+ /* TODO: Simplify device drivers by having this routine rebuild
+ any cmd->use_sg==0 request as a cmd->use_sg==1 request. */
+
+ if (template->dma_map_request) {
+ int dma_dir = scsi_to_pci_dma_dir(cmd->sc_data_direction);
+ if (cmd->use_sg)
+ pci_unmap_sg(cmd->host->pci_dev,
+ (struct scatterlist*)cmd->request_buffer,
+ cmd->use_sg,
+ dma_dir);
+ else if (cmd->request_bufflen)
+ pci_unmap_single(cmd->host->pci_dev,
+ cmd->request_dma_addr,
+ cmd->request_bufflen,
+ dma_dir);
+ }
+
+ if (template->dma_map_sense && cmd->sense_dma_addr)
+ pci_unmap_single(cmd->host->pci_dev,
+ cmd->sense_dma_addr,
+ sizeof(cmd->sense_buffer),
+ PCI_DMA_FROMDEVICE);
+}
+
+static inline int
+scsi_map_dma(Scsi_Cmnd *cmd)
+{
+ const Scsi_Host_Template *template = cmd->host->hostt;
+
+ /* TODO: Simplify device drivers by having this routine rebuild
+ any cmd->use_sg==0 request as a cmd->use_sg==1 request. */
+
+ if (template->dma_map_request) {
+ int dma_dir = scsi_to_pci_dma_dir(cmd->sc_data_direction);
+ if (cmd->use_sg) {
+ cmd->sgcnt_dma = pci_map_sg(cmd->host->pci_dev,
+ (struct scatterlist*)
+ cmd->request_buffer,
+ cmd->use_sg,
+ dma_dir);
+ if (cmd->sgcnt_dma <= 0)
+ return -EBUSY;
+ } else if (cmd->request_bufflen) {
+ cmd->request_dma_addr =
+ pci_map_single(cmd->host->pci_dev,
+ cmd->request_buffer,
+ cmd->request_bufflen,
+ dma_dir);
+ if (!cmd->request_dma_addr)
+ return -EBUSY;
+ }
+ }
+ if (template->dma_map_sense) {
+ cmd->sense_dma_addr = pci_map_single(cmd->host->pci_dev,
+ cmd->sense_buffer,
+ sizeof(cmd->sense_buffer),
+ PCI_DMA_FROMDEVICE);
+ if (!cmd->sense_dma_addr) {
+ scsi_unmap_dma(cmd);
+ return -EBUSY;
+ }
+ }
+ return 0;
+}
+
/*
* Function: scsi_release_request
*
@@ -706,6 +776,7 @@
* length exceeds what the host adapter can handle.
*/
if (CDB_SIZE(SCpnt) <= SCpnt->host->max_cmd_len) {
+ scsi_map_dma(SCpnt);
spin_lock_irqsave(host->host_lock, flags);
rtn = host->hostt->queuecommand(SCpnt, scsi_done);
spin_unlock_irqrestore(host->host_lock, flags);
@@ -1146,6 +1217,7 @@
SCSI_LOG_MLCOMPLETE(1, printk("Ignoring completion of %p due to timeout status", SCpnt));
return;
}
+ scsi_unmap_dma(SCpnt);
spin_lock_irqsave(&scsi_bhqueue_lock, flags);

SCpnt->serial_number_at_timeout = 0;
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