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WhKTDIPzgzr/TZ4=.PK/OiTcG+YVI8m55L/WtlYmvqF2WCHqiRYSlPtyfoue1jcW/ZkzJg4y8wt ivxteSLnyU1Az1hgthvC9lsr8iASW6koJNjhG6fn/xOUkdoeGyuCdV4HQDg9H0FOJOUStfQ0Vg8 UIzwmYpbXMYgCQINHazpqTgFO22UXrxncbWJyk9g5SUkjlOE40njtWrX5qkQLLjnaXXzffPtU6O DzL0kSKjrrSVim2C5BEa/yjkwWvCOEta/kO0z9faJdwoZkHE+NEDB12h0uKm4bD706t4yuyfKAv ++TCDohXgnWh5CN7gcaElaS3LqM9XpGknoLbQkPLIDfkt3MyUtK/R2kaSig== X-TM-Addin-ProductCode: EMS Subject: Re: [virtio-dev] [PATCH v4] virtio-spi: add the device specification On 08.11.23 17:04, Mark Brown wrote: > On Wed, Nov 08, 2023 at 11:42:40PM +0800, Haixu Cui wrote: >> On 11/6/2023 9:33 PM, Mark Brown wrote: >>> On Tue, Oct 24, 2023 at 08:53:46PM +0800, Haixu Cui wrote: >>>> + le16 bus_num; >>>> + le16 chip_select_max_number; >>> That's a *lot* of potential buses and chip selects... >> Here you mean the types of bus_num and chip_select_max_number are "le16"? >> Here I use 16 bits because bus_num and num_chipselect in spi_controller >> structure are both 16 bits. > Yeah, I think that's more for padding/alignment reasons than anything > else. TBH I wondered if just going for a standard int might be better, > it's the combination of picking a smaller type but one that's relatively > large for the domain. We cannot use int at interfaces between device and driver in the virtio world: - "int" is machine dependent, sizeof may be 2, 4 or 8. - It is signed which would be new for the virtio specification. Not done for other devices. - How are signs represented? 2s complement? Strange machines do not use 2s complement. Good is that most of those strange machines have still tubes and are by now obsolete. - The endianess is machine dependent and device and driver may use internally a different native byte ordering. Strange but this is imaginable. le16 is a well defined unsigned type with sizeof 2 bytes and endianess defined as "little endian". > What byte ordering are the multi-byte words in - CPU native or a > particular endianness (eg, wire native)? Virtio uses little endian. (Some data structures in the RPMB device use big endian. But this is an exception and there this was done for a good reason.) --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org