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Re: [Qemu-devel] [PATCH 13/19] libqos/ahci: add ahci command size setter

From: John Snow
Subject: Re: [Qemu-devel] [PATCH 13/19] libqos/ahci: add ahci command size setters
Date: Mon, 02 Feb 2015 16:09:54 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0

On 02/02/2015 05:35 AM, Paolo Bonzini wrote:

On 30/01/2015 19:42, John Snow wrote:
+void ahci_command_set_sizes(AHCICommand *cmd, uint64_t xbytes,
+                            unsigned prd_size)
+    /* Each PRD can describe up to 4MiB, and must not be odd. */
+    g_assert_cmphex(prd_size, <=, 4096 * 1024);
+    g_assert_cmphex(prd_size & 0x01, ==, 0x00);
+    cmd->prd_size = prd_size;
+    cmd->xbytes = xbytes;
+    cmd->fis.count = cpu_to_le16(cmd->xbytes / AHCI_SECTOR_SIZE);

Why do you need cpu_to_le16 here, instead of having it in the function
that writes the command to guest memory?


+    cmd->header.prdtl = size_to_prdtl(cmd->xbytes, cmd->prd_size);

In this case, only the command header had a utility written for it to flip the bits for me. This is part of the FIS, instead, which has no explicit flip-on-write mechanism inside of commit.

So, it's correct, but not terribly consistent.

I can write a fis write helper to make this more internally consistent about when we handle it for the user and when we don't.

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