firmware: tegra: Stop using seq_get_buf()

Opencode a copy of mrq_debug_read() in bpmp_debug_show() so that it
can use seq_write() directly instead of poking holes into the seq_file
abstractions using seq_get_buf().

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Author: Christoph Hellwig

drivers/firmware/tegra/bpmp-debugfs.c

@@ -296,25 +296,61 @@ static int bpmp_debug_show(struct seq_file *m, void *p)
 	struct file *file = m->private;
 	struct inode *inode = file_inode(file);
 	struct tegra_bpmp *bpmp = inode->i_private;
-	char *databuf = NULL;
 	char fnamebuf[256];
 	const char *filename;
-	uint32_t nbytes = 0;
-	size_t len;
-	int err;
-
-	len = seq_get_buf(m, &databuf);
-	if (!databuf)
-		return -ENOMEM;
+	struct mrq_debug_request req = {
+		.cmd = cpu_to_le32(CMD_DEBUG_READ),
+	};
+	struct mrq_debug_response resp;
+	struct tegra_bpmp_message msg = {
+		.mrq = MRQ_DEBUG,
+		.tx = {
+			.data = &req,
+			.size = sizeof(req),
+		},
+		.rx = {
+			.data = &resp,
+			.size = sizeof(resp),
+		},
+	};
+	uint32_t fd = 0, len = 0;
+	int remaining, err;
 
 	filename = get_filename(bpmp, file, fnamebuf, sizeof(fnamebuf));
 	if (!filename)
 		return -ENOENT;
 
-	err = mrq_debug_read(bpmp, filename, databuf, len, &nbytes);
-	if (!err)
-		seq_commit(m, nbytes);
+	mutex_lock(&bpmp_debug_lock);
+	err = mrq_debug_open(bpmp, filename, &fd, &len, 0);
+	if (err)
+		goto out;
+
+	req.frd.fd = fd;
+	remaining = len;
+
+	while (remaining > 0) {
+		err = tegra_bpmp_transfer(bpmp, &msg);
+		if (err < 0) {
+			goto close;
+		} else if (msg.rx.ret < 0) {
+			err = -EINVAL;
+			goto close;
+		}
 
+		if (resp.frd.readlen > remaining) {
+			pr_err("%s: read data length invalid\n", __func__);
+			err = -EINVAL;
+			goto close;
+		}
+
+		seq_write(m, resp.frd.data, resp.frd.readlen);
+		remaining -= resp.frd.readlen;
+	}
+
+close:
+	err = mrq_debug_close(bpmp, fd);
+out:
+	mutex_unlock(&bpmp_debug_lock);
 	return err;
 }